Fix cycle in the plan

Without this change, terraform errors with:
│ Error: Cycle: module.project.google_storage_bucket_iam_member.gcs-sinks-binding, module.project.google_project_iam_member.project-sinks-binding, module.project.google_essential_contacts_contact.contact, module.project.google_bigquery_dataset_iam_member.bq-sinks-binding, module.project.google_project_iam_member.bucket-sinks-binding, module.project (close), module.project.output.sink_writer_identities (expand), local.cluster_sa (expand), module.project.var.iam_bindings_additive (expand), module.project.google_project_iam_member.bindings, module.project.google_logging_project_sink.sink, module.project.google_pubsub_topic_iam_member.pubsub-sinks-binding

The actual error is wrong variable reference.

Closes: #2789

blueprints/gke/patterns/autopilot-cluster/cluster.tf

@@ -22,7 +22,7 @@ locals {
   )
   cluster_sa = (
     local._cluster_sa == "default"
-    ? module.project.service_accounts.default.compute
+    ? module.project.default_service_accounts.compute
     : local._cluster_sa
   )
   cluster_sa_roles = [