Prepare release v5.1.0 (#515)

## heroku/python

### Changed

- Changed the S3 URL used to download Python to use AWS' dual-stack (IPv6 compatible) endpoint. ([#513](#513))

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]
 
+## [5.1.0] - 2026-02-26
+
 ### Changed
 
 - Changed the S3 URL used to download Python to use AWS' dual-stack (IPv6 compatible) endpoint. ([#513](https://github.com/heroku/buildpacks-python/pull/513))
@@ -582,7 +584,8 @@ 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/v5.0.0...HEAD
+[unreleased]: https://github.com/heroku/buildpacks-python/compare/v5.1.0...HEAD
+[5.1.0]: https://github.com/heroku/buildpacks-python/compare/v5.0.0...v5.1.0
 [5.0.0]: https://github.com/heroku/buildpacks-python/compare/v4.1.2...v5.0.0
 [4.1.2]: https://github.com/heroku/buildpacks-python/compare/v4.1.1...v4.1.2
 [4.1.1]: https://github.com/heroku/buildpacks-python/compare/v4.1.0...v4.1.1

buildpack.toml

@@ -2,7 +2,7 @@ api = "0.10"
 
 [buildpack]
 id = "heroku/python"
-version = "5.0.0"
+version = "5.1.0"
 name = "Heroku Python"
 homepage = "https://github.com/heroku/buildpacks-python"
 description = "Heroku's buildpack for Python applications."