Unit tests kick off an ETL when run alone

[zaneselvans]

Describe the bug

On the main branch running the unit tests via our Make recipe works as expected and takes ~1 minute:

make pytest-unit

However, attempting to run the unit tests independently with pytest kicks off an ETL run, which should never happen, and takes a long time:

pytest test/unit

The unit tests that get run as part of our local pre-commit hook don't seem to have this problem. They use the command:

pytest --cov-fail-under=0 --doctest-modules src/pudl test/unit -m "not slow"

Even just telling pytest to report back the durations of the 20 longest tests or not to compile coverage doesn't exhibit the problem:

pytest --durations 20 test/unit
pytest --no-cov test/uni

Could this be an unexpected side effect of our new default pytest / coverage configuration @jdangerx? From #3391?