Issue 41003: test_copyreg: importing numpy changes warnings filters

This issue is similar to bpo-40055: running test_copyreg fails with ENV_CHANGED if numpy is available. Example:

$ ./python -m venv env
$ env/bin/python -m pip install numpy
$ env/bin/python -m test --fail-env-changed -v test_copyreg -m xxxx
== CPython 3.9.0b3+ (heads/getpath_platlibdir39:11462e9847, Jun 11 2020, 17:49:13) [GCC 10.1.1 20200507 (Red Hat 10.1.1-1)]
(...)
Warning -- warnings.filters was modified by test_copyreg
  Before: (140498488250848, [], [])
  After:  (140498488250848, [], [('ignore', re.compile('numpy.ndarray size changed', re.IGNORECASE), <class 'Warning'>, None, 0), ('ignore', re.compile('numpy.ufunc size changed', re.IGNORECASE), <class 'Warning'>, None, 0), ('ignore', re.compile('numpy.dtype size changed', re.IGNORECASE), <class 'Warning'>, None, 0), ('always', None, <class 'numpy.RankWarning'>, None, 0)]) 
(...)

The issue can be replaced by a fake numpy module:

$ cat Lib/numpy.py 
import warnings
warnings.simplefilter('ignore', UserWarning)

New changeset 8362893e3fe083df2ec8bb94c28b1a78383eadbf by Victor Stinner in branch 'master':
bpo-41003: Fix test_copyreg when numpy is installed (GH-20935)
https://github.com/python/cpython/commit/8362893e3fe083df2ec8bb94c28b1a78383eadbf

New changeset b39d41ba1b77f7bc51c4d6f6d0e336693192cb3a by Victor Stinner in branch '3.9':
bpo-41003: Fix test_copyreg when numpy is installed (GH-20935) (GH-20945)
https://github.com/python/cpython/commit/b39d41ba1b77f7bc51c4d6f6d0e336693192cb3a

New changeset 3d974b2fc681ddd0ec722cf631008d5941da52b8 by Victor Stinner in branch '3.8':
bpo-41003: Fix test_copyreg when numpy is installed (GH-20935) (GH-20945) (GH-20946)
https://github.com/python/cpython/commit/3d974b2fc681ddd0ec722cf631008d5941da52b8