Closes #8796 - DoctTest line numbers not found due to method wrapping

[denivyruck]

Hey all!

Used the issue's own test as a test case. Looks a bit bloated so let me know if can be improved!

[nicoddemus]

Hey @denivyruck! 👋

Thanks a lot for this fix. Looks good, could you also please:

1. Add yourself to AUTHORS.
2. Add a changelog/8796.bugfix.rst, describing the fix (in user language), something along these lines:

   Fixed internal error when skipping doctests.

[denivyruck]

Thanks @nicoddemus! Done

[nicoddemus]

Thanks!

[nicoddemus]

Failures in 3.10 are unrelated (#8555 (comment)).

[bluetech]

Thanks for looking at this! Some points:

• We should report it to Python, both so it gets fixed upstream eventually and so we can know if it is the right fix.

• The docstring of _find_lineno should be updated to also mention the new workaround.

• ISTM that _find_lineno is allowed to return None in general, so we should really handle it more gracefully. But that's probably not so simple. Shouldn't block this PR anyway.

[denivyruck]

Thanks @bluetech. I'll open an issue upstream to discuss this probably today or tomorrow. Will let you know then.

For now updated the docstring as suggested 👍

[nicoddemus]

@bluetech can you give this another review? Thanks!