Add environment: pypi to publish job to match trusted publisher

[mstorath]

Summary

Adds environment: pypi to the publish job in .github/workflows/release.yml so the OIDC token claim matches the PyPI trusted-publisher entry (which is registered with environment name pypi).

Why

The first v1.0.1 publish failed with:

invalid-publisher: valid token, but no corresponding publisher
* environment: MISSING

PyPI's pending publisher requires the environment claim to match what's registered. The workflow had no environment: declaration on the publish job, so the claim came through as MISSING. Adding environment: pypi makes the claim present and matching.

What changed

Single 1-line addition in the publish job:

  publish:
    name: Publish to PyPI
    runs-on: ubuntu-latest
    needs: [linux, macos, windows, sdist]
    if: startsWith(github.ref, 'refs/tags/v')
    environment: pypi    # ← added
    steps:

(The PR history contains a misguided rename-then-revert; squash-merging produces just the 1-line net change.)

Required follow-up after merging

The existing v1.0.1 tag points at a commit that doesn't have environment: pypi, so re-running its workflow will still fail. Two user-side steps:

1. Delete the v1.0.1 tag (no PyPI artifact was ever published for it):

   git tag -d v1.0.1
   git push origin --delete v1.0.1

2. Re-tag at the merged main HEAD:

   git checkout main && git pull
   git tag -a v1.0.1 -m "First PyPI release; continues MATLAB version line"
   git push origin v1.0.1

The publish workflow will then run with environment: pypi claim, OIDC matches the publisher, PyPI accepts.

GitHub Environment requirement

Note: trusted publishing with an environment also requires that a GitHub Environment named pypi exists on the repository (Settings → Environments). If it doesn't exist yet, GitHub will fail the job with "Value 'pypi' is not valid" when looking up the environment. Worth checking before re-tagging.

Test plan

• PR Add environment: pypi to publish job to match trusted publisher #4 merged into main
• GitHub Environment pypi exists at https://github.com/mstorath/CSSD/settings/environments
• After re-tagging, the publish job succeeds and pip install cssd==1.0.1 works