Prepare release v3.1.0 (#226)

## heroku/procfile

### Added

- Support for `arm64` and multi-arch images. ([#225](#225))

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

Author: heroku-linguist[bot]

CHANGELOG.md

@@ -7,6 +7,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+## [3.1.0] - 2024-05-02
+
 ### Added
 
 - Support for `arm64` and multi-arch images. ([#225](https://github.com/heroku/buildpacks-procfile/pull/225))
@@ -79,7 +81,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Initial release of Rust procfile buildpack, the old Go buildpack is now archived.
 - Re-write logic of Procfile parsing to match Heroku's behavior, which has different behavior from the Go version (that assumed that a Procfile was YAML syntax).
 
-[unreleased]: https://github.com/heroku/buildpacks-procfile/compare/v3.0.1...HEAD
+[unreleased]: https://github.com/heroku/buildpacks-procfile/compare/v3.1.0...HEAD
+[3.1.0]: https://github.com/heroku/buildpacks-procfile/compare/v3.0.1...v3.1.0
 [3.0.1]: https://github.com/heroku/buildpacks-procfile/compare/v3.0.0...v3.0.1
 [3.0.0]: https://github.com/heroku/buildpacks-procfile/compare/v2.0.2...v3.0.0
 [2.0.2]: https://github.com/heroku/buildpacks-procfile/compare/v2.0.1...v2.0.2

buildpack.toml

@@ -2,7 +2,7 @@ api = "0.10"
 
 [buildpack]
 id = "heroku/procfile"
-version = "3.0.1"
+version = "3.1.0"
 name = "Heroku Procfile"
 homepage = "https://github.com/heroku/buildpacks-procfile"
 description = "Heroku's Procfile buildpack."