Use a repository variable for sleep after request (#1142)

Author: therve

.github/workflows/test_integration.yml

@@ -68,7 +68,7 @@ jobs:
           DD_TEST_CLIENT_APP_KEY: ${{ secrets.DD_CLIENT_APP_KEY }}
           DD_TRACE_ANALYTICS_ENABLED: "true"
           RECORD: "none"
-          SLEEP_AFTER_REQUEST: "${{ secrets.SLEEP_AFTER_REQUEST }}"
+          SLEEP_AFTER_REQUEST: "${{ vars.SLEEP_AFTER_REQUEST }}"
       - name: Post failure status check
         if: failure() && github.event_name == 'pull_request' && contains(github.event.pull_request.head.ref, 'datadog-api-spec/generated/')
         uses: DataDog/github-actions/post-status-check@v2