Remove unused pytest skip

[dstansby]

I originally included the pytest.skip because in rare cases (I think debug builds of Cpython??) docstrings can return None instead of their contents. I think this is rare enough that we don't need to care about it, and it's better just adding a # type: ignore comment instead of a pytest.skip.

I'm hoping this gets code coverage back up to 100% again to fix #646

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.92%. Comparing base (29995e3) to head (018d0c0).
Report is 43 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #651      +/-   ##
==========================================
+ Coverage   99.81%   99.92%   +0.11%     
==========================================
  Files          62       62              
  Lines        2712     2721       +9     
==========================================
+ Hits         2707     2719      +12     
+ Misses          5        2       -3     

Files with missing lines	Coverage Δ
numcodecs/tests/test_zarr3.py	100.00% <100.00%> (+2.17%)	⬆️

... and 3 files with indirect coverage changes

[jakirkham]

Thanks David! 🙏

This seems reasonable

If we think we do need this condition, we could also add a # pragma: no cover