gh-64063: Clarify safe usage of Queue in multiprocessing "Using a remote manager" section

[PrinceNaroliya]

Summary

This PR updates the documentation in `library/multiprocessing.rst` under the Using a remote manager section.

Changes

• Replaced direct `Queue()` usage with `Manager().Queue()`.
• Updated local process example for consistency with remote manager usage.
• Ensured examples reflect safe multiprocessing practices.

Impact

• Clarifies correct usage for beginners following the docs.
• Prevents confusion around proxy objects and remote accessibility.
• Aligns the Using a remote manager section with other multiprocessing examples.

Related Issue

Fixes #64063

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📚 Documentation preview 📚: https://cpython-previews--138454.org.readthedocs.build/

• Issue: [doc] multiprocessing Proxy docs need locking semantics explained #64063

[StanFromIreland]

Hello! I have fixed your title for you to what it should be, I suggest you read these helpful pages in the devguide.

[PrinceNaroliya]

Thank you for fixing the title, and for sharing the devguide links.
I’ll make sure to follow the title and contribution guidelines properly in my future PRs.