Prevent git diff output printed in pr builder

.github/workflows/pr-builder.yml

@@ -42,7 +42,7 @@ jobs:
     - name: Install dependencies
       run: |
         yarn
-        git diff --exit-code
+        git diff --exit-code > /dev/null
         if [ $? -ne 0 ]; then
           echo "There are modified files after running yarn."
           exit 1