Run mypy on the test cases and test scripts (#7746)

tests/pytype_test.py

@@ -19,8 +19,8 @@ import sys
 import traceback
 from collections.abc import Sequence
 
-from pytype import config as pytype_config, load_pytd
-from pytype.pytd import typeshed
+from pytype import config as pytype_config, load_pytd  # type: ignore[import]
+from pytype.pytd import typeshed  # type: ignore[import]
 
 TYPESHED_SUBDIRS = ["stdlib", "stubs"]
 TYPESHED_HOME = "TYPESHED_HOME"