Downgrade libcnb

Since it includes the breaking deprecation change.

libcnb updates are supposed to be in a separate PR, but
Dependabot has a bug (race condition?) that means they
sometimes are combined in the main update PR.

buildpacks/ruby/Cargo.toml

@@ -16,8 +16,8 @@ glob = "0.3"
 indoc = "2"
 # libcnb has a much bigger impact on buildpack behaviour than any other dependencies,
 # so it's pinned to an exact version to isolate it from lockfile refreshes.
-libcnb = "=0.22.0"
-libherokubuildpack = { version = "=0.23.0", default-features = false, features = ["digest"] }
+libcnb = "=0.21.0"
+libherokubuildpack = { version = "=0.21.0", default-features = false, features = ["digest"] }
 rand = "0.8"
 # TODO: Consolidate on either the regex crate or the fancy-regex crate, since this repo currently uses both.
 regex = "1"
@@ -31,4 +31,4 @@ magic_migrate = "0.2"
 toml = "0.8"
 
 [dev-dependencies]
-libcnb-test = "=0.22.0"
+libcnb-test = "=0.21.0"

commons/Cargo.toml

@@ -24,8 +24,8 @@ indoc = "2"
 lazy_static = "1"
 # libcnb has a much bigger impact on buildpack behaviour than any other dependencies,
 # so it's pinned to an exact version to isolate it from lockfile refreshes.
-libcnb = "=0.22.0"
-libherokubuildpack = { version = "=0.23.0", default-features = false, features = ["command"] }
+libcnb = "=0.21.0"
+libherokubuildpack = { version = "=0.21.0", default-features = false, features = ["command"] }
 regex = "1"
 serde = "1"
 sha2 = "0.10"
@@ -36,6 +36,6 @@ walkdir = "2"
 [dev-dependencies]
 filetime = "0.2"
 indoc = "2"
-libcnb-test = "=0.22.0"
+libcnb-test = "=0.21.0"
 pretty_assertions = "1"
 toml = "0.8"