fix: release workflow runs unit tests only

Integration tests (browser rendering with Cuprite/Selenium) are covered
by the test workflow's matrix jobs. The release workflow only needs to
verify gem code correctness before publishing — unit tests are sufficient
and don't have flaky browser baselines.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: pftg

.github/workflows/release.yml

@@ -35,7 +35,7 @@ jobs:
           fi
 
       - name: Test
-        run: bundle exec rake test
+        run: bundle exec rake test:unit
 
       - name: Create tag
         run: |