fix: Added variables as instructed by @root

.gitlab-ci.yml

@@ -142,6 +142,9 @@ test-scheme:
     # Enable per-build-network so that service aliases are also
     # usable in the service containers themselves.
     FF_NETWORK_PER_BUILD: 1
+    # https://stackoverflow.com/questions/71228282/could-not-resolve-host-when-trying-to-access-service-in-gitlab
+    DOCKER_HOST: "tcp://docker:2375"
+    DOCKER_TLS_CERTDIR: ""
   parallel:
     matrix:
       # see https://schemathesis.readthedocs.io/en/stable/cli.html#cmdoption-schemathesis-run-c