Prepare release v308 (#1903)

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

Author: heroku-linguist[bot]

CHANGELOG.md

@@ -2,6 +2,9 @@
 
 ## [Unreleased]
 
+
+## [v308] - 2025-09-19
+
 - Updated Poetry from 2.1.4 to 2.2.0. ([#1900](https://github.com/heroku/heroku-buildpack-python/pull/1900))
 - Updated uv from 0.8.15 to 0.8.18. ([#1899](https://github.com/heroku/heroku-buildpack-python/pull/1899) and [#1901](https://github.com/heroku/heroku-buildpack-python/pull/1901))
 - Improved performance of Python build cache saving. ([#1902](https://github.com/heroku/heroku-buildpack-python/pull/1902))
@@ -1329,7 +1332,8 @@ Default Python is now latest 2.7.10. Updated pip and Distribute.
 - Setuptools updated to v16.0
 - pip updated to v7.0.1
 
-[unreleased]: https://github.com/heroku/heroku-buildpack-python/compare/v307...main
+[unreleased]: https://github.com/heroku/heroku-buildpack-python/compare/v308...main
+[v308]: https://github.com/heroku/heroku-buildpack-python/compare/v307...v308
 [v307]: https://github.com/heroku/heroku-buildpack-python/compare/v306...v307
 [v306]: https://github.com/heroku/heroku-buildpack-python/compare/v305...v306
 [v305]: https://github.com/heroku/heroku-buildpack-python/compare/v304...v305