patched GetCurrentTime to use correct timezone-aware datetime

[b-d-e]

Addresses #19161 by addressing the deprecation warning.

See python 3.12 release notes for motivating python change:

datetime: datetime.datetime’s utcnow() and utcfromtimestamp() are deprecated and will be removed in a future version. Instead, use timezone-aware objects to represent datetimes in UTC: respectively, call now() and fromtimestamp() with the tz parameter set to datetime.UTC. (Contributed by Paul Ganssle in gh-103857.)

Existing unit tests should handle these changes.

Without this, this warning appears when using protobuf:

.venv/lib/python3.12/site-packages/google/protobuf/internal/well_known_types.py:178: DeprecationWarning: datetime.datetime.utcnow() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.now(datetime.UTC).
  self.FromDatetime(datetime.datetime.utcnow())

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[b-d-e]

This won't work as is under Python 3.8.x, but that version has passed end-of-life support from Python - I don't know what the intended future support from protobuf is?

If desired, I can add a conditional check that changes the behaviour based on if version <3.9, using the old method if so.