[master] Fix datetime.datetime.utcnow() deprecated in Python 3.12

[chloekaii]

What does this PR do?

This changes all instances of datetime.utcnow() to datetime.now(tz=timezone.utc).

What issues does this PR fix or reference?

Fixes: #65604

Merge requirements satisfied?

[NOTICE] Bug fixes or features added to Salt require tests.

• [ ] Docs
• [ ] Changelog - https://docs.saltproject.io/en/master/topics/development/changelog.html
• [ ] Tests written/updated

Commits signed with GPG?

No

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See GitHub's page on GPG signing for more information about signing commits with GPG.

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[max-arnold]

I think this might be not backward compatible, because utcnow() returns a naive datetime, and now(tz=datetime.UTC) returns a timezone-aware one.

[twangboy]

To create a naive datetime

from datetime import datetime, UTC
datetime.now(UTC).replace(tzinfo=None)

[marmarek]

I think this might be not backward compatible, because utcnow() returns a naive datetime, and now(tz=datetime.UTC) returns a timezone-aware one.

That's the point of this deprecation warning, no? To stop using non-timezone-aware objects.