avoid file clobbering in okify

[braingram]

Removes use of --flat in okify_regtests that can result in file clobbering and failure to okify all differences.

Closes https://github.com/spacetelescope/jwst/issues/8969

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? (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 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

news fragment change types...

- ``changes/.general.rst``: infrastructure or miscellaneous change - ``changes/.docs.rst`` - ``changes/.stpipe.rst`` - ``changes/.datamodels.rst`` - ``changes/.scripts.rst`` - ``changes/.fits_generator.rst`` - ``changes/.set_telescope_pointing.rst`` - ``changes/.pipeline.rst`` ## stage 1 - ``changes/.group_scale.rst`` - ``changes/.dq_init.rst`` - ``changes/.emicorr.rst`` - ``changes/.saturation.rst`` - ``changes/.ipc.rst`` - ``changes/.firstframe.rst`` - ``changes/.lastframe.rst`` - ``changes/.reset.rst`` - ``changes/.superbias.rst`` - ``changes/.refpix.rst`` - ``changes/.linearity.rst`` - ``changes/.rscd.rst`` - ``changes/.persistence.rst`` - ``changes/.dark_current.rst`` - ``changes/.charge_migration.rst`` - ``changes/.jump.rst`` - ``changes/.clean_flicker_noise.rst`` - ``changes/.ramp_fitting.rst`` - ``changes/.gain_scale.rst`` ## stage 2 - ``changes/.assign_wcs.rst`` - ``changes/.badpix_selfcal.rst`` - ``changes/.msaflagopen.rst`` - ``changes/.nsclean.rst`` - ``changes/.imprint.rst`` - ``changes/.background.rst`` - ``changes/.extract_2d.rst`` - ``changes/.master_background.rst`` - ``changes/.wavecorr.rst`` - ``changes/.srctype.rst`` - ``changes/.straylight.rst`` - ``changes/.wfss_contam.rst`` - ``changes/.flatfield.rst`` - ``changes/.fringe.rst`` - ``changes/.pathloss.rst`` - ``changes/.barshadow.rst`` - ``changes/.photom.rst`` - ``changes/.pixel_replace.rst`` - ``changes/.resample_spec.rst`` - ``changes/.residual_fringe.rst`` - ``changes/.cube_build.rst`` - ``changes/.extract_1d.rst`` - ``changes/.resample.rst`` ## stage 3 - ``changes/.assign_mtwcs.rst`` - ``changes/.mrs_imatch.rst`` - ``changes/.tweakreg.rst`` - ``changes/.skymatch.rst`` - ``changes/.exp_to_source.rst`` - ``changes/.outlier_detection.rst`` - ``changes/.tso_photometry.rst`` - ``changes/.stack_refs.rst`` - ``changes/.align_refs.rst`` - ``changes/.klip.rst`` - ``changes/.spectral_leak.rst`` - ``changes/.source_catalog.rst`` - ``changes/.combine_1d.rst`` - ``changes/.ami.rst`` ## other - ``changes/.wfs_combine.rst`` - ``changes/.white_light.rst`` - ``changes/.cube_skymatch.rst`` - ``changes/.engdb_tools.rst`` - ``changes/.guider_cds.rst``

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 64.53%. Comparing base (3401d49) to head (eba67c0). Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
jwst/scripts/okify_regtests.py	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #8970 +/- ## ========================================== - Coverage 64.53% 64.53% -0.01% ========================================== Files 375 375 Lines 38745 38744 -1 ========================================== - Hits 25003 25002 -1 Misses 13742 13742 ```

:umbrella: View full report in Codecov by Sentry.
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