Fix cancel workflow run (#856)

Author: sunmou99

.github/workflows/integration_tests.yml

@@ -112,7 +112,7 @@ jobs:
             else
               echo "::set-output name=requested_tests::expanded"
             fi
-          elif [[ "${{ github.event.action }}" == "closed" && ${{ github.event.pull_request.merged }} = true ]]; then
+          elif [[ "${{ github.event.action }}" == "closed" && "${{ github.event.pull_request.merged == true}}" == "true" ]]; then
             echo "::set-output name=trigger::postsubmit_trigger"
             echo "::set-output name=pr_number::${{ github.event.pull_request.number }}"
             echo "::set-output name=requested_tests::auto"