Fix test_ne in test_cmp.py for Python 3.13

[frenzymadness]

Summary

Compiler in Python 3.13+ strips indents from docstrings so they need to be compared without it for new Pythons.

Tested with 3.13.0a4

Fixes: #1228

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[frenzymadness]

I found the attr._compat module so I use it now.

[hynek]

Super, díky!