Update screenshots path in GitHub Actions

Since we upgraded to Rails 7.0 in commmit 8596f1539, the screenshots
started to be stored in `tmp/capybara`, so the step uploading
screenshots wasn't doing anything.

.github/workflows/tests.yml

@@ -72,7 +72,7 @@ jobs:
         uses: actions/upload-artifact@v4
         with:
           name: screenshots
-          path: tmp/screenshots
+          path: tmp/capybara/
   coveralls:
     permissions:
       contents: none