ci: Build test-snaps in publish-release job to include it in NPM publishing

[Mrtenz]

Following #3679, we want test-snaps to be publishable to NPM. Currently only TypeScript packages are built, so test-snaps wouldn't be published properly. I've added an extra step to build test-snaps before running the NPM publish job.

---

Note

Updates the publish-release workflow to install dependencies in a dedicated step and build @metamask/test-snaps so it’s included in release artifacts/NPM publish.

• CI (GitHub Actions):
  • publish-release job:
    • Add dedicated Install dependencies step (yarn install --immutable).
    • Build all packages with yarn build.
    • New step to build @metamask/test-snaps (yarn workspace @metamask/test-snaps build) so artifacts include it.

^{Written by Cursor Bugbot for commit 4ffbc25. This will update automatically on new commits. Configure here.}

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.28%. Comparing base (313198b) to head (4ffbc25).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3712   +/-   ##
=======================================
  Coverage   98.28%   98.28%           
=======================================
  Files         418      418           
  Lines       12152    12152           
  Branches     1876     1876           
=======================================
  Hits        11943    11943           
  Misses        209      209           

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