try to fix the kwargs var

.gitlab-ci.yml

@@ -13,7 +13,7 @@ variables:
   TESTING_URL: http://134.94.199.220:7001/home
   TESTING_DOMAIN: zam10220.zam.kfa-juelich.de
   AIRFLOW_TESTUSER: "airflow"
-  AIRFLOW__SECRETS__BACKEND_KWARGS: '{"url" : "https://zam10036.zam.kfa-juelich.de", "user" : "${DATACAT_TESTING_USERNAME}", "password" : "${DATACAT_TESTING_PASSWORD}"}'
+  AIRFLOW__SECRETS__BACKEND_KWARGS: $TESTING_AIRFLOW__SECRETS__BACKEND_KWARGS
   AIRFLOW__SECRETS__BACKEND: datacat_integration.secrets.DatacatSecretsBackend
   DOCKER_TLS_CERTDIR: ""