Fix CI: allow Gemfile.lock update for Rails version matrix

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

Author: ursm

.github/workflows/test.yml

@@ -26,4 +26,7 @@ jobs:
         with:
           ruby-version: ${{ matrix.ruby }}
           bundler-cache: true
+        env:
+          BUNDLE_GEMFILE: ${{ github.workspace }}/Gemfile
+          BUNDLE_FROZEN: 'false'
       - run: bundle exec rake test