gh-114990: Add missing mixin methods in collections.abc's document

[aisk]

• Issue: gh-114990

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📚 Documentation preview 📚: https://cpython-previews--114991.org.readthedocs.build/

[blaisep]

@rhettinger , FYI, I'm just scrubbing the PR list and this seems like a small change to align the doc with the code.

[miss-islington-app[bot]]

Thanks @aisk for the PR, and @willingc for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12, 3.13. 🐍🍒⛏🤖

[miss-islington-app[bot]]

Thanks @aisk for the PR, and @willingc for merging it 🌮🎉.. I'm working now to backport this PR to: 3.13. 🐍🍒⛏🤖

[miss-islington-app[bot]]

Thanks @aisk for the PR, and @willingc for merging it 🌮🎉.. I'm working now to backport this PR to: 3.12. 🐍🍒⛏🤖

[bedevere-app[bot]]

GH-128535 is a backport of this pull request to the 3.13 branch.

[bedevere-app[bot]]

GH-128536 is a backport of this pull request to the 3.12 branch.