BUG: fix common arg handling

[cpelley]

43 didn't quite fix the issue it was intended to address.

I must have left changes locally (i.e. not pushed up all changes to github). CI pytest failures were being hidden by our use of pipe.

• Fixed argument handling behaviour (tests pass demonstrating this locally and via CI).
• Fixed pytest failures being hidden (see test ${PIPESTATUS[0]} -eq 0 in the CI workflow).
• Fixed test sensitivity to argparse version in dagrunner/tests/utils/test_function_to_parse.py.
• Disabled logging integration tests running in CI (to be investigated and re-enabled in #39).
  • This will cause a 'The test coverage has decreased' comment via the CI which can be ignored.

Issues

• https://github.com/MetOffice/improver_suite/issues/2253

[github-actions[bot]]

The test coverage has decreased from 84% to 78% (commit SHA: 73929cdab6f1e311d25f8f011a1f17f96a2381b7). Please review test coverage. Report uploaded as artifact.

[cpelley]

The test coverage has decreased from 84% to 78%...

Safe to ignore this. Cause: ignoring logging integration tests (which don't work in CI right now). Will be re-enabled in #39.