Handle no-changes case in homebrew-release workflow

If the formula is already up to date (same version/SHA, no bottle block),
exit gracefully instead of failing on empty commit.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: sbryngelson

.github/workflows/homebrew-release.yml

@@ -157,6 +157,13 @@ jobs:
           git config user.email "github-actions[bot]@users.noreply.github.com"
 
           git add Formula/mfc.rb
+
+          # Check if there are changes to commit
+          if git diff --cached --quiet; then
+            echo "::notice::No changes to commit - formula already up to date for v${VERSION}"
+            exit 0
+          fi
+
           git commit -m "Update MFC to v${VERSION}"
 
           echo "Pushing to homebrew-mfc..."