Remove uv.lock workflow workaround once release-please#2693 is released

[jlopez]

Context

We manually update `uv.lock` in the release workflow as a workaround for the lack of native `uv.lock` support in release-please (see googleapis/release-please#2561).

The fix is being tracked in googleapis/release-please#2693, which adds a dedicated `UvLock` updater to release-please.

What to do

Once release-please ships a version that includes #2693:

1. Bump the `googleapis/release-please-action` version in .github/workflows/release.yml
2. Remove the three steps added after the release-please action step (checkout, setup-uv, update uv.lock)
3. Verify the release-please PR for the next release includes the `uv.lock` update natively