[3.12] gh-127805: Clarify Formatter initialization in logging.rst. (GH-127850)

[miss-islington]

(cherry picked from commit 5d66c55)

Co-authored-by: UV [email protected]

• Issue: Logger formatter class initialization state clarification  #127805

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📚 Documentation preview 📚: https://cpython-previews--130393.org.readthedocs.build/

[ghost]

All commit authors signed the Contributor License Agreement.

[vsajip]

@Uvi-12 Did you change your email address or something? Apparently we've lost track of your CLA signature, so can you please re-sign? This and the backport PR for 3.13 are affected. Thanks!

[terryjreedy]

The addition is "The fmt argument must be a :class:Formatter instance or None." This nice addition is too substantial to 'steal' (merge under a new name) but IMO not substantial enough to go to lots of extra work to merge if @Uvi-12 never responds. DItto for 3.13 backport.

[Uvi-12]

Sorry for the late. I have signed the CLA, is there anything I will have to do after that?