Add stree:check to CI

Author: kddnewton

.github/workflows/main.yml

@@ -22,7 +22,9 @@ jobs:
         bundler-cache: true
         ruby-version: ${{ matrix.ruby }}
     - name: Test
-      run: bundle exec rake test
+      run: |
+        bundle exec rake test
+        bundle exec rake stree:check
   automerge:
     name: AutoMerge
     needs: ci