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

diff --git a/tests/test_docstring_options.py b/tests/test_docstring_options.py
index 0dbca60..80ade0f 100644
--- a/tests/test_docstring_options.py
+++ b/tests/test_docstring_options.py
@@ -1,3 +1,4 @@
+# -*- coding: utf-8 -*-
 from pybind11_tests import docstring_options as m