ci(perf): Speed up release pipeline by removing full git clones (#11790)
## Summary
Four jobs in the release workflow use `fetch-depth: 0`, each taking ~45s
to clone entire repo history. This eliminates those full clones, saving
~3 minutes of wall time per release.
- **check-skip**: Removed the checkout entirely. Uses `gh api` to find
the last `version.txt` commit and compare changes.
- **stage**: Shallow clone + explicit `git fetch --tags` (only tag refs
are needed, not full history).
- **create-release-tag**: Removed `fetch-depth: 0` — only creates and
pushes a tag.
- **create-release-pr**: Replaced `git log` changelog generation with
`gh api .../compare` endpoint, removing the need for history and the
`Fetch main and tags` step.