💥 Make TemporaryFileUpload.submission non-nullable

[sergei-maertens]

Part of #3283

We've provided a transition period from Open Forms 2.7, which ensures that a submission is stored. Support for legacy uploads is now removed.

The celery background jobs should by now have deleted all the old unclaimed uploads, unless absurdly large retention values have been set.

Checklist

Check off the items that are completed or not relevant.

• Impact on features

  • Checked copying a form
  • Checked import/export of a form
  • Config checks in the configuration overview admin page
  • Problem detection in the admin email digest is handled

• Release management

  • I have labelled the PR as "needs-backport" accordingly

• I have updated the translations assets (you do NOT need to provide translations)

  • Ran ./bin/makemessages_js.sh
  • Ran ./bin/compilemessages_js.sh

• Commit hygiene

  • Commit messages refer to the relevant Github issue
  • Commit messages explain the "why" of change, not the how

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.62%. Comparing base (3e7b959) to head (6adb90d).
Report is 28 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4894      +/-   ##
==========================================
- Coverage   96.62%   96.62%   -0.01%     
==========================================
  Files         757      757              
  Lines       25945    25942       -3     
  Branches     3419     3419              
==========================================
- Hits        25069    25066       -3     
  Misses        613      613              
  Partials      263      263              

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[sergei-maertens]

-> need to add an upgrade check script

[vaszig]

I think there are some more pieces left like here:
https://github.com/open-formulieren/open-forms/blob/master/src/openforms/formio/components/vanilla.py#L387

[sergei-maertens]

I think there are some more pieces left like here: https://github.com/open-formulieren/open-forms/blob/master/src/openforms/formio/components/vanilla.py#L387

is it not showing up in the diff for you? I've remove this check since I came across it when CTRL + F on 'legacy'.