Capture guard output and fail on ERROR log lines in development mode test

Co-authored-by: rubensworks <440384+rubensworks@users.noreply.github.com>

Author: Copilot

.github/workflows/integration.yml

@@ -35,9 +35,12 @@ jobs:
         working-directory: my-article
       - name: Test development mode
         run: |
-          bundle exec guard --no-interactions &
+          rm -f guard.log
+          bundle exec guard --no-interactions > guard.log 2>&1 &
           GUARD_PID=$!
           sleep 5
+          cat guard.log
+          if grep -q ' - ERROR - ' guard.log; then exit 1; fi
           kill -0 $GUARD_PID
           kill $GUARD_PID
           wait $GUARD_PID || true