`inspect._getmembers` duplicates self type in `mro` for no good reason

[sobolevn]

This line https://github.com/python/cpython/blame/4d82f628c44490d6fbc3f6998d2473d1304d891f/Lib/inspect.py#L540 has this logic mro = (object,) + getmro(object)

I don't think this is correct:

1. getmro returns MRO including self type
2. We waste time on doing this
3. It might backfire at some moment, now it works because of how MRO is used later

Introduced in 86a8a9a

Linked PRs

• gh-99677: Deduplicate self-type in mro in inspect._getmembers #99678