Prepare release v4.0.2 (#373)

## heroku/ruby

### Fixed

- Ruby pre-release verssions like `3.4.0.rc1` now work as expected. ([#372](#372))
- Layer metadata deserialization to Rust structs is now using `#[serde(deny_unknown_fields)]` this prevents the accidental scenario where metadata containing a superset of fields could accidentally be deserialized to the wrong struct. It's unlikely this is currently happening with the current buildpack, but it's a possibly-observable difference so it's being listed ([#371](#371))

Co-authored-by: heroku-linguist[bot] <136119646+heroku-linguist[bot]@users.noreply.github.com>

buildpacks/ruby/CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [4.0.2] - 2024-12-16
+
 ### Fixed
 
 - Ruby pre-release verssions like `3.4.0.rc1` now work as expected. ([#372](https://github.com/heroku/buildpacks-ruby/pull/372))
@@ -78,7 +80,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Initial version of Ruby buildpack in Rust (https://github.com/heroku/buildpacks-ruby/pull/93)
 - Version 2.0.0 for the first release is not a typo. There was an issue in pack where a builder with the same name and version number would reuse artifacts left on image from [prior runs which caused issues](https://github.com/buildpacks/pack/issues/1322#issuecomment-1038241038). There were prior releases of `heroku/ruby` CNB from different sources that triggered this problem. To ensure no one would encounter that issue we developed and released using a version we know has not been used before. Version 2.0 was the first major version without a prior release of `heroku/ruby` CNB from any source.
 
-[unreleased]: https://github.com/heroku/buildpacks-ruby/compare/v4.0.1...HEAD
+[unreleased]: https://github.com/heroku/buildpacks-ruby/compare/v4.0.2...HEAD
+[4.0.2]: https://github.com/heroku/buildpacks-ruby/compare/v4.0.1...v4.0.2
 [4.0.1]: https://github.com/heroku/buildpacks-ruby/compare/v4.0.0...v4.0.1
 [4.0.0]: https://github.com/heroku/buildpacks-ruby/compare/v3.0.0...v4.0.0
 [3.0.0]: https://github.com/heroku/buildpacks-ruby/compare/v2.1.3...v3.0.0

buildpacks/ruby/buildpack.toml

@@ -2,7 +2,7 @@ api = "0.10"
 
 [buildpack]
 id = "heroku/ruby"
-version = "4.0.1"
+version = "4.0.2"
 name = "Heroku Ruby"
 homepage = "https://github.com/heroku/buildpacks-ruby"
 description = "Heroku's buildpack for Ruby applications."