[TEST] Use lightweight chart for Helm OCI tests

This may reduce the load on CI runners by using a sleeper chart instead
of a more heavyweight setup with a front-end server and a Redis
instance.

e2e/assets/single-cluster/helm-oci.yaml

@@ -4,6 +4,7 @@ metadata:
   name: helm
 spec:
   repo: https://github.com/rancher/fleet-test-data
+  branch: helm-oci-lightweight-chart
   paths:
   - helm-oci
   targets:

e2e/single-cluster/single_cluster_test.go

@@ -41,7 +41,7 @@ var _ = Describe("Single Cluster Deployments", func() {
 				Eventually(func() string {
 					out, _ := k.Namespace("fleet-helm-oci-example").Get("pods")
 					return out
-				}).Should(ContainSubstring("frontend-"))
+				}).Should(ContainSubstring("sleeper-"))
 			})
 		})