build: align release workflow with sample-plugin standard

[farhan]

What changed

Updates .github/workflows/release.yml to match the current sample-plugin release standard, as established in openedx/sample-plugin#57.

Why

The openedx org now has GitHub immutable releases enabled, which freezes a release's assets the moment it is published. Our flow (like sample-plugin's before #57) published the release first and then attached the distributions in a separate python-semantic-release/publish-action step — which GitHub now rejects with HTTP 422 (Cannot upload assets to an immutable release).

In sample-plugin this silently produced asset-less releases from v3.6.1 onward, and started hard-failing the release job once python-semantic-release v10.6.0+ stopped swallowing the upload error. This repo runs the same flow and would hit the identical failure.

What sample-plugin#57 did (and this PR mirrors)

• vcs_release: "false" on the python-semantic-release step — it still commits, tags, pushes and builds, but no longer creates the GitHub Release itself.
• publish-action is replaced by a gh release create step that creates the release as a draft, uploads the dist/* assets, and only then publishes it — the sequence immutable releases require. PSR's generated notes are reused via the release_notes output so the release body is unchanged.

Adaptations for this repo:

• Bump python-semantic-release v10.6.1 → v10.6.2.
• Pin pypa/gh-action-pypi-publish to a commit SHA (v1.14.2) instead of the floating release/v1 tag. OIDC trusted publishing is preserved (no API token).

Notes

Draft PR — the release workflow only runs on merge to main, so end-to-end behaviour can't be exercised on the branch (same caveat as #57, which validated itself by releasing on merge).

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.17%. Comparing base (a14ce68) to head (fdc7a44).

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #77   +/-   ##
=======================================
  Coverage   82.17%   82.17%           
=======================================
  Files          48       48           
  Lines        1419     1419           
  Branches      110      110           
=======================================
  Hits         1166     1166           
  Misses        221      221           
  Partials       32       32           

Flag	Coverage Δ
unittests	82.17% <ø> (ø)

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