JP-3667: Add safeguards for NSClean on background/imprint members

[melanieclarke]

Resolves JP-3667

Follow up to #8786 to fix some unexpected interactions between badpix_selfcal and nsclean, causing a failure in the badpix_selfcal regression tests. If badpix_selfcal is run, the background members are datamodels instead of filenames.

I also noticed in testing this that setting the output file for nsclean on the background/imprint members caused them to be saved by default, so I added a check for that as well.

Tasks

• request a review from someone specific, to avoid making the maintainers review every PR
• add a build milestone, i.e. Build 11.3 (use the latest build if not sure)
• Does this PR change user-facing code / API?
  • add an entry to CHANGES.rst within the relevant release section (otherwise add the no-changelog-entry-needed label to this PR)
  • update or add relevant tests
  • update relevant docstrings and / or docs/ page
  • start a regression test and include a link to the running job (click here for instructions)
    • Do truth files need to be updated ("okified")?
      • after the reviewer has approved these changes, run okify_regtests to update the truth files
• if a JIRA ticket exists, make sure it is resolved properly

[melanieclarke]

Regtests here:
https://plwishmaster.stsci.edu:8081/job/RT/job/JWST-Developers-Pull-Requests/1735/

[emolter]

LGTM pending regression tests showing no unexpected failures

[codecov]

Codecov Report

Attention: Patch coverage is 6.25000% with 15 lines in your changes missing coverage. Please review.

Project coverage is 61.76%. Comparing base (da9691d) to head (9c68fc3).
Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
jwst/pipeline/calwebb_spec2.py	6.25%	15 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #8809   +/-   ##
=======================================
  Coverage   61.75%   61.76%           
=======================================
  Files         377      377           
  Lines       38750    38785   +35     
=======================================
+ Hits        23931    23955   +24     
- Misses      14819    14830   +11     

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[hayescr]

LGTM as well, sorry I missed this on the last one.