I can reproduce the leak with the following test, stored as Lib/test/test_leak.py:
---
from test import support
import unittest

class Tests(unittest.TestCase):
    def test_import_fresh(self):
        support.import_fresh_module('importlib.machinery',
            fresh=('importlib',),
            blocked=('_frozen_importlib', '_frozen_importlib_external'))
---

Extract of "./python -m test -R 3:3 test_leak" output:
---
test_leak leaked [6303, 6299, 6303] references, sum=18905
test_leak leaked [2022, 2020, 2022] memory blocks, sum=6064
---