gh-65453: Docs - clarify AttributeError behaviour on PropertyMock

[ziima]

Fixed at EuroPython 24 sprints.

• Issue: gh-65453

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📚 Documentation preview 📚: https://cpython-previews--121666.org.readthedocs.build/

[ghost]

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[miss-islington-app[bot]]

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

[bedevere-app[bot]]

GH-121968 is a backport of this pull request to the 3.13 branch.

[bedevere-app[bot]]

GH-121969 is a backport of this pull request to the 3.12 branch.