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

diff --git a/tests/test_exceptions.py b/tests/test_exceptions.py
index ac2b360..053e7d4 100644
--- a/tests/test_exceptions.py
+++ b/tests/test_exceptions.py
@@ -1,3 +1,4 @@
+# -*- coding: utf-8 -*-
 import pytest
 
 from pybind11_tests import exceptions as m