[3.14] gh-145591: Move slicing note to __getitem__ (GH-145606)

[miss-islington]

(cherry picked from commit 2114da9)

Co-authored-by: Ali Towaiji 145403626+Towaiji@users.noreply.github.com

• Issue: Slicing in Wrong Place in Docs #145591

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📚 Documentation preview 📚: https://cpython-previews--145760.org.readthedocs.build/

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[encukou]

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[Towaiji]

Hey @encukou!
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