refactor: use explicit conversion in f-strings

tests/stress/benchmark_running_server.py

@@ -134,7 +134,7 @@ async def benchmark_get_projects(base_url, headers, project_count, iterations=10
                 else:
                     print(f"  Iteration {i + 1}: ERROR {response.status_code}")
             except Exception as e:
-                print(f"  Iteration {i + 1}: Exception - {type(e).__name__}: {str(e)}")
+                print(f"  Iteration {i + 1}: Exception - {type(e).__name__}: {e!s}")
 
     # Cleanup test projects
     if project_count > 0: