Resolve datetime deprecation warnings

[emmanuel-ferdman]

PR Summary

This PR fixes the datetime deprecation warnings that can be viewed in the CI logs:

test/sasl/test_msk.py::test_aws_msk_iam_client_temporary_credentials
  /home/runner/work/kafka-python/kafka-python/test/sasl/test_msk.py:13: DeprecationWarning: datetime.datetime.utcfromtimestamp() is deprecated and scheduled for removal in a future version. Use timezone-aware objects to represent datetimes in UTC: datetime.datetime.fromtimestamp(timestamp, datetime.UTC).
    now = datetime.datetime.utcfromtimestamp(1629321911)

[dpkp]

Can we modify to keep support for python2.7 ?

[emmanuel-ferdman]

@dpkp If Python2.7 support is required, I think we could go with something like:

import sys

if sys.version_info >= (3, 3):
    # Use timezone-aware datetime for Python 3.3+
    now = datetime.datetime.fromtimestamp(1629321911, datetime.timezone.utc)
else:
    # Fallback to utcfromtimestamp for Python 2.7
    now = datetime.datetime.utcfromtimestamp(1629321911)

Not the most elegant solution, but it should get the job done while supporting Python 2.7 and future Python versions. What do you think?

[dpkp]

That's great, thanks!

[dpkp]

Thanks!