13403: Disable assertion rewriting for external modules

Author: Tusenka

testing/test_assertrewrite.py

@@ -23,6 +23,8 @@
 from unittest import mock
 import zipfile
 
+from _pytest.monkeypatch import MonkeyPatch
+
 import _pytest._code
 from _pytest._io.saferepr import DEFAULT_REPR_MAX_SIZE
 from _pytest.assertion import util