gh-85453: Fix 'time zone' spelling issues across datetime.rst

[uatach]

Another pull request based on PR #21447, this one focused on fixing spelling issues on occurrences of 'time zone'.

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📚 Documentation preview 📚: https://cpython-previews--118449.org.readthedocs.build/

• Issue: Wrong/missing code formats in datetime documentation #85453

[uatach]

@erlend-aasland there are similar issues for occurrences of datetime like this one, but I was not sure if I should include them in the same PR

[pganssle]

I think timezone is also an acceptable spelling, if that's what we've been consistently using, we should probably continue using that.

Alternatively, we could differentiate between datetime.timezone (the class) and the more abstract notion of a "time zone" by including the space for the abstract notion, but I'm more inclined to mark out references to the class with backticks / class references rather than a spelling difference.

[uatach]

I think timezone is also an acceptable spelling, if that's what we've been consistently using, we should probably continue using that.

I'm not sure... the IANA database uses "time zone" and both Wikipedia and The Free Dictionary redirect "timezone" to "time zone"... so maybe "timezone" isn't even valid spelling but people use it anyway?

Alternatively, we could differentiate between datetime.timezone (the class) and the more abstract notion of a "time zone" by including the space for the abstract notion, but I'm more inclined to mark out references to the class with backticks / class references rather than a spelling difference.

Yes, I tried to differentiate all of them (the class and the instances and objects of the class) from the abstract concept.