Bump uv from 0.9.17 to 0.9.21 (#2003)

* Bump uv from 0.9.17 to 0.9.21

Bumps [uv](https://github.com/astral-sh/uv) from 0.9.17 to 0.9.21.
- [Release notes](https://github.com/astral-sh/uv/releases)
- [Changelog](https://github.com/astral-sh/uv/blob/main/CHANGELOG.md)
- [Commits](astral-sh/uv@0.9.17...0.9.21)

---
updated-dependencies:
- dependency-name: uv
  dependency-version: 0.9.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

* Add changelog entry

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Ed Morley <501702+edmorley@users.noreply.github.com>

Author: dependabot[bot]

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## [Unreleased]
 
+- Updated uv from 0.9.17 to 0.9.21. ([#2003](https://github.com/heroku/heroku-buildpack-python/pull/2003))
 
 ## [v325] - 2025-12-10
 

requirements/uv.txt

@@ -1 +1 @@
-uv==0.9.17
+uv==0.9.21