Add the ExternalName test to the CI pipeline (but without repetition).

In test/e2e.sh, we run the test twice, to confirm that VMOD dynamic
picks up the changed IP for the DNS name. For now, just run the test
once in the pipeline.

.gitlab-ci.yml

@@ -259,6 +259,14 @@ example:tls:sni:
     - ./verify.sh
     - ./undeploy.sh
 
+example:externalname
+  extends: .integration-tests
+  script:
+    - cd ../examples/externalname
+    - ./deploy.sh
+    - ./verify.sh
+    - ./undeploy.sh
+
 .integration-tests:
   needs: ["build:controller"]
   stage: e2e