Replaced calls to deprecated `datetime.datetime.utcnow()` with
`datetime.datetime.now(datetime.UTC)` in `tests/unit/job/test_base.py`.

Replaced calls to deprecated `datetime.datetime.utcfromtimestamp()` with
`datetime.datetime.fromtimestamp(timestamp, datetime.UTC)` in
`tests/unit/job/helpers.py`.

These changes address the specific warnings identified in the issue
for these two files.