Pin astral-sh/ruff-action to a specific commit

The GitHub docs recommend pinning third-party actions to specific
commits for security hardening purposes.

Author: correctmost

.github/workflows/ruff.yaml

@@ -5,4 +5,4 @@ jobs:
         runs-on: ubuntu-latest
         steps:
             - uses: actions/checkout@v4
-            - uses: astral-sh/ruff-action@v3
+            - uses: astral-sh/ruff-action@39f75e526a505e26a302f8796977b50c13720edf