Prepare release v326

[heroku-linguist]

Commits since the last release:

• Unpin GDAL version in tests (Unpin GDAL version in tests #1998)
• Bump sigstore/cosign/cosign from v3.0.2 to v3.0.3 in /builds (Bump sigstore/cosign/cosign from v3.0.2 to v3.0.3 in /builds #2002)
• Bump rubocop from 1.81.7 to 1.82.1 in the ruby-dependencies group (Bump rubocop from 1.81.7 to 1.82.1 in the ruby-dependencies group #2001)
• Bump uv from 0.9.17 to 0.9.21 (Bump uv from 0.9.17 to 0.9.21 #2003)

For the full diff, see the compare view:
v325...main

[edmorley]

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

- Updated uv from 0.9.17 to 0.9.21. ([#2003](https://github.com/heroku/heroku-buildpack-python/pull/2003))

Deploy as v326 [y/n]? y

Creating GitHub release...
https://github.com/heroku/heroku-buildpack-python/releases/tag/v326

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

 Version Released At              Status    
 ─────── ──────────────────────── ───────── 
 326     2026-01-05T11:08:14.206Z published