Prepare release v291

[heroku-linguist]

Commits since the last release:

• Bump the ruby-dependencies group with 2 updates (Bump the ruby-dependencies group with 2 updates #1825)
• Further reduce team review request noise from CODEOWNERS (Further reduce team review request noise from CODEOWNERS #1826)
• Bump uv from 0.7.13 to 0.7.19 (Bump uv from 0.7.13 to 0.7.19 #1827)
• Bump uv from 0.7.19 to 0.7.20 (Bump uv from 0.7.19 to 0.7.20 #1829)
• Change the python/ directory related warnings to errors (Change the python/ directory related warnings to errors #1830)

For the full diff, see the compare view:
v290...main

[edmorley]

$ make publish
Checking environment...
Checking buildpack versions in sync...
Extracting changelog entry for this release...

- Updated uv from 0.7.13 to 0.7.20. ([#1827](https://github.com/heroku/heroku-buildpack-python/pull/1827) and [#1829](https://github.com/heroku/heroku-buildpack-python/pull/1829))
- The build now errors if the Python buildpack has been run multiple times in the same build. This replaces the warning displayed since December 2024. ([#1830](https://github.com/heroku/heroku-buildpack-python/pull/1830))
- The build now errors if an existing `.heroku/python/` directory is found in the app source. This replaces the warning displayed since December 2024. ([#1830](https://github.com/heroku/heroku-buildpack-python/pull/1830))

Deploy as v291 [y/n]? y

Creating GitHub release...
https://github.com/heroku/heroku-buildpack-python/releases/tag/v291

Publishing to the Heroku Buildpack Registry...
Two-factor code: ********************************************
Publishing buildpack heroku/python... done
Publishing buildpack was successful

 Version Released At              Status    
 ─────── ──────────────────────── ───────── 
 291     2025-07-10T14:25:54.166Z published