style: pre-commit fixes

Author: pre-commit-ci[bot]

tests/pybind11_tests.h

@@ -115,4 +115,4 @@ class TestContext {
 private:
     TestContext(std::string context) : context(context) {}
     std::string context;
-};
+};

tests/test_class.py

@@ -519,6 +519,7 @@ def test_all_type_info_multithreaded():
     #         "instance allocation failed: new instance has no pybind11-registered base types");
     # }
     import threading
+
     from pybind11_tests import TestContext
 
     class Context(TestContext):