CI: scope stdout debug callback to kubespray test runs

The debug callback apparently breaks using ansible-playbook in
pre-commit, so scope the variables to only where we're using it instead.

.gitlab-ci.yml

@@ -10,7 +10,6 @@ variables:
   FAILFASTCI_NAMESPACE: 'kargo-ci'
   GITLAB_REPOSITORY: 'kargo-ci/kubernetes-sigs-kubespray'
   ANSIBLE_FORCE_COLOR: "true"
-  ANSIBLE_STDOUT_CALLBACK: "debug"
   MAGIC: "ci check this"
   GS_ACCESS_KEY_ID: $GS_KEY
   GS_SECRET_ACCESS_KEY: $GS_SECRET
@@ -43,6 +42,8 @@ before_script:
       - cluster-dump/
   needs:
     - pipeline-image
+  variables:
+    ANSIBLE_STDOUT_CALLBACK: "debug"
 
 .job-moderated:
   extends: .job