Update launch stage for GPU on WorkerPools from ALPHA to BETA (#15058)

Author: kminsu-google

mmv1/templates/terraform/examples/cloudrunv2_worker_pool_gpu.tf.tmpl

@@ -2,7 +2,7 @@ resource "google_cloud_run_v2_worker_pool" "{{$.PrimaryResourceId}}" {
   name     = "{{index $.Vars "cloud_run_worker_pool_name"}}"
   location = "us-central1"
   deletion_protection = false
-  launch_stage = "ALPHA"
+  launch_stage = "BETA"
 
   template {
     containers {