Show all errors on test run

[mccalluc]

Right now CI checks are are in three separate steps:

      - name: Pre-commit (format checks)
        run: pre-commit run --all-files

      - name: Check deployments
        run: python scripts/check.py --skip check_urls

      - name: Unit tests
        run: pytest -vv

It would be better to collect all the errors on the first run, probably by having a test that runs check.py and pre-commit as subprocesses.

• Prompted by the iteration required for Add Additional 2020 Census Deployments #158.