chore: update argocd version in test/e2e/prereqs/argocd/kustomization.yaml (#863)

Signed-off-by: Cheng Fang <cfang@redhat.com>

Author: chengfang

test/e2e/prereqs/argocd/kustomization.yaml

@@ -1,5 +1,5 @@
 resources:
-  - https://github.com/argoproj/argo-cd/manifests/cluster-install?ref=v2.1.5
+  - https://github.com/argoproj/argo-cd/manifests/cluster-install?ref=stable
   - repository.yaml
 
 patches: