added CLUSTER_USER env variable to gh actions

Author: leszekamz

.github/workflows/cpp-libpq-integ-tests.yml

@@ -77,6 +77,7 @@ jobs:
       env:
         CLUSTER_ENDPOINT: ${{ secrets.CPP_LIBPQ_CLUSTER_ENDPOINT }}
         REGION: ${{ secrets.CPP_LIBPQ_CLUSTER_REGION }}
+        CLUSTER_USER: admin
         LD_LIBRARY_PATH: /lib/x86_64-linux-gnu:/home/runner/work/aurora-dsql-samples/aurora-dsql-samples/cpp/libpq/aws-sdk-install/lib
       run: |
         ./libpq_example