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

diff --git a/tests/test_modules.py b/tests/test_modules.py
index 2552838..7e21005 100644
--- a/tests/test_modules.py
+++ b/tests/test_modules.py
@@ -1,3 +1,4 @@
+# -*- coding: utf-8 -*-
 from pybind11_tests import modules as m
 from pybind11_tests.modules import subsubmodule as ms
 from pybind11_tests import ConstructorStats