Switch to heroku/builder:22 in docs and tests

Since it supersedes `heroku/buildpacks:20`:
https://github.com/heroku/builder#heroku-builder-images

Whilst updating the example build output in the README, I noticed
that the specified commands were incorrect (eg wrong buildpack path),
so those have been fixed.

In addition, I've switched the hello world example to use the wildcard
stack, since the code is not stack-specific, and it will save us having to
remember to update it in the future.

Lastly, updating the Ruby example buildpack to `heroku/builder:22`
revealed that the buildpack was actually broken and relying on
system Ruby, so that buildpack has been excluded from using the
new builder until that is resolved:
#398

README.md

@@ -87,7 +87,7 @@ version = "0.1.0"
 name = "My Buildpack"
 
 [[stacks]]
-id = "heroku-20"
+id = "*"
 ```
 
 That's all we need! We can now move on to finally write some buildpack code!
@@ -179,14 +179,14 @@ In your project directory, run `cargo libcnb package` to start packaging:
 $ cargo libcnb package
 INFO - Reading buildpack metadata...
 INFO - Found buildpack libcnb-examples/my-buildpack with version 0.1.0.
-INFO - Building buildpack binary (x86_64-unknown-linux-musl)...
-Compiling my-buildpack v0.1.0 (/Users/manuel.fuchs/projects/my-buildpack)
+INFO - Determining automatic cross-compile settings...
+INFO - Building binaries (x86_64-unknown-linux-musl)...
 # Omitting compilation output...
-Finished dev [unoptimized + debuginfo] target(s) in 2.67s
+    Finished dev [unoptimized + debuginfo] target(s) in 4.29s
 INFO - Writing buildpack directory...
-INFO - Successfully wrote buildpack directory: target/debug/libcnb-examples_my-buildpack_0.1.0 (53.1M)
+INFO - Successfully wrote buildpack directory: target/buildpack/debug/libcnb-examples_my-buildpack (55.5M)
 INFO - Packaging successfully finished!
-INFO - Hint: To test your buildpack locally with pack, run: pack build my-image --buildpack target/debug/libcnb-examples_my-buildpack_0.1.0 --path /path/to/application
+INFO - Hint: To test your buildpack locally with pack, run: pack build my-image --buildpack target/buildpack/debug/libcnb-examples_my-buildpack --path /path/to/application
 ```
 
 If you get errors with hints about how to install required tools to cross-compile from your host platform to the
@@ -201,31 +201,33 @@ application code at all, we just create an empty directory and use that as our a
 
 ```shell
 $ mkdir bogus-app
-$ pack build my-image --buildpack target/debug/libcnb-examples_my-buildpack_0.1.0 --path bogus-app --builder heroku/buildpacks:20
-20: Pulling from heroku/buildpacks
-Digest: sha256:04e8ea7a1f482f289d432d9518edcfaaf9f3a10432cd1b624e58225f22e7c416
-Status: Image is up to date for heroku/buildpacks:20
-20: Pulling from heroku/pack
-Digest: sha256:21ea4b85bc937b47e017bf43136a5295ec08e093e3c210b20e69e9c1b0f2bd57
-Status: Image is up to date for heroku/pack:20
+$ pack build my-image --buildpack target/buildpack/debug/libcnb-examples_my-buildpack --path bogus-app --builder heroku/builder:22
+22: Pulling from heroku/builder
+Digest: sha256:0e1db52b480805c63b793a1c0155ea30cabffbf7977f722c88dc42cef750a1d1
+Status: Image is up to date for heroku/builder:22
+22-cnb: Pulling from heroku/heroku
+Digest: sha256:3fd7866f22dcbcd3a72c7ab4b47728dcfbaacfa9730341d0fb10665f63d93788
+Status: Image is up to date for heroku/heroku:22-cnb
+===> ANALYZING
+Previous image with name "my-image" not found
 ===> DETECTING
 libcnb-examples/my-buildpack 0.1.0
-===> ANALYZING
-Skipping buildpack layer analysis
+===> RESTORING
 ===> BUILDING
 Hello World!
-Build runs on stack heroku-20!
+Build runs on stack heroku-22!
 ===> EXPORTING
-Reusing 1/1 app layer(s)
-Reusing layer 'launcher'
-Reusing layer 'config'
-Reusing layer 'process-types'
+Adding layer 'launch.sbom'
+Adding 1/1 app layer(s)
+Adding layer 'launcher'
+Adding layer 'config'
+Adding layer 'process-types'
 Adding label 'io.buildpacks.lifecycle.metadata'
 Adding label 'io.buildpacks.build.metadata'
 Adding label 'io.buildpacks.project.metadata'
 Setting default process type 'web'
 Saving my-image...
-*** Images (d4f67a828236):
+*** Images (24eed75bb2e6):
       my-image
 Successfully built image my-image
 ```

examples/execd/tests/integration_test.rs

@@ -12,7 +12,7 @@ use libcnb_test::{assert_contains, IntegrationTest};
 #[test]
 #[ignore]
 fn basic() {
-    IntegrationTest::new("heroku/buildpacks:20", "test-fixtures/empty-app").run_test(|context| {
+    IntegrationTest::new("heroku/builder:22", "test-fixtures/empty-app").run_test(|context| {
         context
             .prepare_container()
             .start_with_shell_command("env", |container| {

libcnb-test/README.md

@@ -19,7 +19,7 @@ use libcnb_test::{IntegrationTest, BuildpackReference, assert_contains};
 
 #[test]
 fn test() {
-    IntegrationTest::new("heroku/buildpacks:20", "test-fixtures/app")
+    IntegrationTest::new("heroku/builder:22", "test-fixtures/app")
         .buildpacks(vec![
             BuildpackReference::Other(String::from("heroku/openjdk")),
             BuildpackReference::Crate,

libcnb-test/src/container_context.rs

@@ -40,7 +40,7 @@ impl<'a> PrepareContainerContext<'a> {
     /// ```no_run
     /// use libcnb_test::IntegrationTest;
     ///
-    /// IntegrationTest::new("heroku/buildpacks:20", "test-fixtures/app").run_test(|context| {
+    /// IntegrationTest::new("heroku/builder:22", "test-fixtures/app").run_test(|context| {
     ///     context
     ///         .prepare_container()
     ///         .env("FOO", "FOO_VALUE")
@@ -60,7 +60,7 @@ impl<'a> PrepareContainerContext<'a> {
     /// ```no_run
     /// use libcnb_test::IntegrationTest;
     ///
-    /// IntegrationTest::new("heroku/buildpacks:20", "test-fixtures/app").run_test(|context| {
+    /// IntegrationTest::new("heroku/builder:22", "test-fixtures/app").run_test(|context| {
     ///     context
     ///         .prepare_container()
     ///         .envs(vec![("FOO", "FOO_VALUE"), ("BAR", "BAR_VALUE")])

libcnb-test/src/lib.rs

@@ -39,7 +39,7 @@ use std::process::{Command, Stdio};
 /// # fn call_test_fixture_service(addr: std::net::SocketAddr, payload: &str) -> Result<String, ()> {
 /// #    unimplemented!()
 /// # }
-/// IntegrationTest::new("heroku/buildpacks:20", "test-fixtures/app")
+/// IntegrationTest::new("heroku/builder:22", "test-fixtures/app")
 ///     .buildpacks(vec![
 ///         BuildpackReference::Other(String::from("heroku/openjdk")),
 ///         BuildpackReference::Crate,
@@ -153,7 +153,7 @@ impl IntegrationTest {
     /// ```no_run
     /// use libcnb_test::IntegrationTest;
     ///
-    /// IntegrationTest::new("heroku/buildpacks:20", "test-fixtures/app")
+    /// IntegrationTest::new("heroku/builder:22", "test-fixtures/app")
     ///     .env("ENV_VAR_ONE", "VALUE ONE")
     ///     .env("ENV_VAR_TWO", "SOME OTHER VALUE")
     ///     .run_test(|context| {
@@ -174,7 +174,7 @@ impl IntegrationTest {
     /// ```no_run
     /// use libcnb_test::IntegrationTest;
     ///
-    /// IntegrationTest::new("heroku/buildpacks:20", "test-fixtures/app")
+    /// IntegrationTest::new("heroku/builder:22", "test-fixtures/app")
     ///     .envs(vec![("ENV_VAR_ONE", "VALUE ONE"), ("ENV_VAR_TWO", "SOME OTHER VALUE")])
     ///     .run_test(|context| {
     ///         // ...
@@ -203,7 +203,7 @@ impl IntegrationTest {
     /// ```no_run
     /// use libcnb_test::IntegrationTest;
     ///
-    /// IntegrationTest::new("heroku/buildpacks:20", "test-fixtures/app")
+    /// IntegrationTest::new("heroku/builder:22", "test-fixtures/app")
     ///     .app_dir_preprocessor(|app_dir| {
     ///         std::fs::remove_file(app_dir.join("Procfile")).unwrap()
     ///     })
@@ -235,7 +235,7 @@ impl IntegrationTest {
     /// ```no_run
     /// use libcnb_test::{IntegrationTest, assert_contains};
     ///
-    /// IntegrationTest::new("heroku/buildpacks:20", "test-fixtures/app")
+    /// IntegrationTest::new("heroku/builder:22", "test-fixtures/app")
     ///     .run_test(|context| {
     ///         assert_contains!(context.pack_stdout, "---> Ruby Buildpack");
     ///         assert_contains!(context.pack_stdout, "---> Installing bundler");
@@ -354,7 +354,7 @@ impl<'a> IntegrationTestContext<'a> {
     /// ```no_run
     /// use libcnb_test::IntegrationTest;
     ///
-    /// IntegrationTest::new("heroku/buildpacks:20", "test-fixtures/empty-app").run_test(|context| {
+    /// IntegrationTest::new("heroku/builder:22", "test-fixtures/empty-app").run_test(|context| {
     ///     context.prepare_container().start_with_default_process(|container| {
     ///         // ...
     ///     });