Backport PR #9602 on branch release/1.19.x (JP-4047: Update regtests for niriss and nircam wfss)

[meeseeksmachine]

Backport PR #9602: JP-4047: Update regtests for niriss and nircam wfss

[codecov]

Codecov Report

❌ Patch coverage is 0% with 8 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (release/1.19.x@ee6c8ce). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
jwst/datamodels/utils/tests/test_flat_multispec.py	0.00%	6 Missing ⚠️
jwst/datamodels/utils/flat_multispec.py	0.00%	2 Missing ⚠️

Additional details and impacted files

@@               Coverage Diff                @@
##             release/1.19.x   #9634   +/-   ##
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  Coverage                  ?   0.00%           
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  Files                     ?     368           
  Lines                     ?   37224           
  Branches                  ?       0           
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  Hits                      ?       0           
  Misses                    ?   37224           
  Partials                  ?       0           

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