CI: add_pmbootstrap_to_import_path: add import (MR 802)

Fix error on my machine:
	AttributeError: module 'importlib' has no attribute 'util'

.gitlab-ci/testcases/add_pmbootstrap_to_import_path/__init__.py

@@ -6,6 +6,7 @@ import shutil
 import sys
 import os
 import importlib
+import importlib.util
 from distutils.sysconfig import get_python_lib