Prepare release v0.18.0 (#273)

## heroku/python

### Added

- The Python version can now be configured using a `.python-version` file. Both the `3.X` and `3.X.Y` version forms are supported. ([#272](#272))

### Changed

- pip is now only available during the build, and is longer included in the final app image. ([#264](#264))
- Improved the error messages shown when an end-of-life or unknown Python version is requested. ([#272](#272))

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]
 
+## [0.18.0] - 2024-09-17
+
 ### Added
 
 - The Python version can now be configured using a `.python-version` file. Both the `3.X` and `3.X.Y` version forms are supported. ([#272](https://github.com/heroku/buildpacks-python/pull/272))
@@ -210,7 +212,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Initial implementation. ([#3](https://github.com/heroku/buildpacks-python/pull/3))
 
-[unreleased]: https://github.com/heroku/buildpacks-python/compare/v0.17.1...HEAD
+[unreleased]: https://github.com/heroku/buildpacks-python/compare/v0.18.0...HEAD
+[0.18.0]: https://github.com/heroku/buildpacks-python/compare/v0.17.1...v0.18.0
 [0.17.1]: https://github.com/heroku/buildpacks-python/compare/v0.17.0...v0.17.1
 [0.17.0]: https://github.com/heroku/buildpacks-python/compare/v0.16.0...v0.17.0
 [0.16.0]: https://github.com/heroku/buildpacks-python/compare/v0.15.0...v0.16.0

buildpack.toml

@@ -2,7 +2,7 @@ api = "0.10"
 
 [buildpack]
 id = "heroku/python"
-version = "0.17.1"
+version = "0.18.0"
 name = "Heroku Python"
 homepage = "https://github.com/heroku/buildpacks-python"
 description = "Heroku's buildpack for Python applications."