[renovate] Update mongo Docker tag to v8

See merge request !1040

Co-authored-by: Renovate Bot <renovate@danet.fbi.h-da.de>

.gitlab/ci/.test.yml

@@ -14,7 +14,7 @@ integration-test-gosdn:
         INTEGRATION_TEST_RABBITMQ_HOSTNAME: rabbitmq
         INTEGRATION_TEST_CONTROLLER_URL: gosdn:55055
     services:
-      - name: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/mongo:7
+      - name: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/mongo:8
         alias: mongo
       - name: ${CI_DEPENDENCY_PROXY_GROUP_IMAGE_PREFIX}/rabbitmq:4-management
         alias: rabbitmq