metadata for release `1.15.1` (`B11.0rc2`)

[zacharyburnett]

regtest running at https://github.com/spacetelescope/RegressionTests/actions/runs/9812819013

[nden]

Please add this release to the README. Probably worth making an entry in the CHANGES file saying something like

ramp_fitting:
- Fix bugs in the C algorithm Poisson variance calculation when provided with an average dark current. [stcal#269]

- Use the C extension with multiprocessing. [stcal#268]

Is requirements-sdp updated on the release branch?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 59.56%. Comparing base (d02ac25) to head (8797df6).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #8629 +/- ## ======================================= Coverage 59.56% 59.56% ======================================= Files 391 391 Lines 39285 39285 ======================================= Hits 23402 23402 Misses 15883 15883 ```

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[zacharyburnett]

Is requirements-sdp updated on the release branch?

Not yet, I'll update that when doing the release

[zacharyburnett]

changing the scope of this PR to release metadata generally