testing/py3-glob2: fix pytest 8 & invalid escape sequence, and build with gpep517

Last activity upstream was 5 years ago. So, this MR adds patches that address these 2 bug reports:

• Invalid escape sequence warning: https://github.com/miracle2k/python-glob2/issues/25

• Pytest 8 compatibility: https://github.com/miracle2k/python-glob2/issues/30