Prepare release v312 (#1923)

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]
 
+
+## [v312] - 2025-10-05
+
 - Updated uv from 0.8.20 to 0.8.23. ([#1916](https://github.com/heroku/heroku-buildpack-python/pull/1916) and [#1922](https://github.com/heroku/heroku-buildpack-python/pull/1922))
 
 ## [v311] - 2025-09-30
@@ -1350,7 +1353,8 @@ 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/v311...main
+[unreleased]: https://github.com/heroku/heroku-buildpack-python/compare/v312...main
+[v312]: https://github.com/heroku/heroku-buildpack-python/compare/v311...v312
 [v311]: https://github.com/heroku/heroku-buildpack-python/compare/v310...v311
 [v310]: https://github.com/heroku/heroku-buildpack-python/compare/v309...v310
 [v309]: https://github.com/heroku/heroku-buildpack-python/compare/v308...v309