JP-3458: Moving ramp_fit CI tests from JWST to STCAL.

[kmacdonald-stsci]

Resolves JP-3458

This PR addresses moves CI tests from JWST to STCAL.

This PR is in conjunction with https://github.com/spacetelescope/jwst/pull/8060, which removed these tests from JWST.

Checklist

• [x] added entry in CHANGES.rst (either in Bug Fixes or Changes to API)
• [ ] updated relevant tests
• [ ] updated relevant documentation
• [ ] updated relevant milestone(s)
• [x] added relevant label(s)

[codecov[bot]]

Codecov Report

Attention: 56 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
tests/test_ramp_fitting_cases.py	85.26% <85.26%> (ø)

... and 1 file with indirect coverage changes

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