fix astrocut downstream tests

[braingram]

Description

astrocut moved their asdf tests in spacetelescope/astrocut#149

This PR updates the astrocut downstream tests here to use --pyargs which looks to be the expected way to run these tests based on:
https://github.com/spacetelescope/astrocut/blob/9c5aebecd806705e3942bd9204dd8be705b38059/tox.ini#L65
also rather than calling just the asdf tests (which breaks every time they rename/reorg the test files) this PR also just runs all astrocut tests.

Tasks

• run pre-commit on your machine
• run pytest on your machine
• Does this PR add new features and / or change user-facing code / API? (if not, label with no-changelog-entry-needed)
  • write news fragment(s) in changes/: echo "changed something" > changes/<PR#>.<changetype>.rst (see below for change types)
  • update relevant docstrings and / or docs/ page
  • for any new features, add unit tests

news fragment change types...

• changes/<PR#>.feature.rst: new feature
• changes/<PR#>.bugfix.rst: bug fix
• changes/<PR#>.doc.rst: documentation change
• changes/<PR#>.removal.rst: deprecation or removal of public API
• changes/<PR#>.general.rst: infrastructure or miscellaneous change

[braingram]

astrocut downstream tests now passed. As this PR only changes that line will merge.