fix: resolve detached HEAD warning in swift-format workflow

- Add ref parameter to actions/checkout to avoid detached HEAD state
- Uses github.head_ref for PRs, github.ref_name for pushes
- Eliminates warning from git-auto-commit-action

Author: coenttb

.github/workflows/swift-format.yml

@@ -18,6 +18,8 @@ jobs:
       contents: write
     steps:
       - uses: actions/checkout@v5
+        with:
+          ref: ${{ github.head_ref || github.ref_name }}
 
       - name: Cache swift-format
         id: cache-swift-format