enable headless behave tests

.gitlab-ci.yml

@@ -61,7 +61,7 @@ behave-login:
   image: ${CI_REGISTRY_IMAGE}/login_provider_ci_test:${CI_COMMIT_REF_NAME}
   script:
     - cd login_provider/test/behave/
-    - python3 -m behave -D url=http://login_provider:5000 -D email=example@oas.example.net -D password=password
+    - python3 -m behave -D headless=True -D url=http://login_provider:5000 -D email=example@oas.example.net -D password=password
   artifacts:
     paths:
       - login_provider/test/behave/screenshots/