[GHA] Only format Swift files that are in Git index

.github/workflows/pull_request_soundness.yml

@@ -57,6 +57,7 @@ jobs:
         fetch-depth: 0
     - name: Mark the workspace as safe
       # https://github.com/actions/checkout/issues/766
+      if: ${{ env.GITHUB_WORKSPACE != '' }}
       run: git config --global --add safe.directory ${GITHUB_WORKSPACE}
     - name: Run API breakage check
       run: swift package diagnose-api-breaking-changes origin/main
@@ -125,10 +126,11 @@ jobs:
       uses: actions/checkout@v4
     - name: Mark the workspace as safe
     # https://github.com/actions/checkout/issues/766
+      if: ${{ env.GITHUB_WORKSPACE != '' }}
       run: git config --global --add safe.directory ${GITHUB_WORKSPACE}
     - name: Run format lint check
-      run:  swift format lint --strict --recursive --parallel .
+      run:  git ls-files -z '*.swift' | xargs -0 swift format lint --strict --parallel
     - name: Run format and check for modified files
       run: |
-        swift format format --parallel --recursive --in-place .
+        git ls-files -z '*.swift' | xargs -0 swift format format --parallel --in-place
         git diff-index --quiet HEAD