refactor: prefer f-strings to other format/concatentation styles (#8474)

tests/stubtest_stdlib.py

@@ -46,7 +46,7 @@ def run_stubtest(typeshed_dir: Path) -> int:
             "\nNB: stubtest output depends on the Python version (and system) it is run with. "
             "See README.md for more details.\n"
             "NB: We only check positional-only arg accuracy for Python 3.10.\n"
-            "\nCommand run was: {}\n".format(" ".join(cmd)),
+            f"\nCommand run was: {' '.join(cmd)}\n",
             file=sys.stderr,
         )
         print("\n\n", file=sys.stderr)