Check for unstaged changes during GitHub Actions “Test” workflow

.github/workflows/test.yaml

@@ -39,6 +39,10 @@ jobs:
       - name: Functional tests (Chromium)
         run: npm run karma
 
-      # Run linter last so other tests run even if there is a code formatting error
+      # Run linter after tests to prevent failure due to code formatting error
       - name: Lint
         run: npm run standard
+
+      # Run postbuild with check for unstaged changes
+      - name: Check for unstaged changes
+        run: npm run postbuild