ci: GHA basic format & pre-commit (#2309)

diff --git a/tests/test_gil_scoped.py b/tests/test_gil_scoped.py
index 1548337..1307712 100644
--- a/tests/test_gil_scoped.py
+++ b/tests/test_gil_scoped.py
@@ -1,3 +1,4 @@
+# -*- coding: utf-8 -*-
 import multiprocessing
 import threading
 from pybind11_tests import gil_scoped as m