Fix MIRI LRS spec3 regtest setup

[hbushouse]

This PR fixes the setup in the MIRI LRS slit spec3 regression test, to avoid problems that arise when things intentionally change. The problem is related to the fact that the test has 4 iterations to it, generating the same s2d product each time. At the same time it was using one of the truth files as WCS input information, from which to generate some of the later iterations of s2d products. So when the pipeline code or ref files change, the test was still using the WCS from the old truth file to generate the new s2d products. Then when "okify_regtests" tries to use the new s2d products to update the truth, it's using a result that was generated from the old truth file and hence doesn't actually accomplish the appropriate update.

So I've changed the mechanics of the test to use the WCS from the s2d product generated by the first iteration as the input to all the subsequent iterations. That way the later iterations are using the "new" WCS info.

Truth files on artifactory have been updated by hand to also get things into a good starting configuration going forward.

Checklist for PR authors (skip items if you don't have permissions or they are not applicable)

• added entry in CHANGES.rst within the relevant release section
• updated or added relevant tests
• updated relevant documentation
• added relevant milestone
• added relevant label(s)
• ran regression tests, post a link to the Jenkins job below.
  How to run regression tests on a PR
• All comments are resolved
• Make sure the JIRA ticket is resolved properly

[hbushouse]

I've confirmed that the updated test module and truth files now pass when running the test locally. Also started a full regtest run at https://plwishmaster.stsci.edu:8081/job/RT/job/JWST-Developers-Pull-Requests/1507

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.13%. Comparing base (b7e0b10) to head (bdb676d).
Report is 311 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8543      +/-   ##
==========================================
+ Coverage   58.02%   58.13%   +0.10%     
==========================================
  Files         388      388              
  Lines       38977    38973       -4     
==========================================
+ Hits        22617    22656      +39     
+ Misses      16360    16317      -43     

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