Botocore deprecation warning

[gchqdev227]

The tests emit the following deprecation warning:

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)

This is coming from botocore. This PR is looking to address it, but in the meantime we should catch this warning.

[gchqdev227]

To replicate quickly, run the following:

$ python3 -m unittest discover -k test_fetch_secret_latest_version
.venv/lib/python3.12/site-packages/botocore/auth.py:425: 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).
  datetime_now = datetime.datetime.utcnow()