chore: Update fetch-depth comment

[keelerm84]

Summary

• Fix incorrect comment on fetch-depth in GitHub Actions workflow(s)
• The old comment implied fetch-depth: 0 was for getting only the current version, when it actually fetches full history

Test plan

• Verify CI workflows still pass

🤖 Generated with Claude Code

---

Note

Low Risk
Comment-only change in a GitHub Actions workflow; no behavioral impact.

Overview
Updates the comment on actions/checkout’s fetch-depth: 0 in release-please.yml to correctly state that a full git history is required for changelog generation.

^{Written by Cursor Bugbot for commit 9456370. This will update automatically on new commits. Configure here.}