BUG: Handle NA in assert_numpy_array_equal
- [x] closes #31881
- [x] tests added / passed
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

I think in the the case where we have NA we want to use identity rather than equality for checking when two arrays are equal.
I think worth back porting to 1.0.2 > I think worth back porting to 1.0.2

Yes, it's internal only, but since other fixes that will be backported might want to rely on this testing functionality, let's backport @dsaxton Thanks!