style: fix Black formatting for pia_search_facets.py

- Add missing trailing comma in function signature
- Ensure compatibility with Black 25.1.0 used in GitHub Actions
- Fix failing lint check in CI/CD pipeline

Author: dividor

src/pia_mcp_server/tools/pia_search_facets.py

@@ -28,7 +28,7 @@
 
 
 async def handle_pia_search_facets(
-    arguments: Dict[str, Any]
+    arguments: Dict[str, Any],
 ) -> List[types.TextContent]:
     """Handle PIA search facets requests."""
     try: