[CI] Upgrade ARC to v0.12.1

This is the latest version. The cluster has been upgraded, so now comitting
the new TF to not mess with anyone's state now that the GCS state bucket has
been upgraded.

Author: boomanaiden154

premerge/main.tf

@@ -132,7 +132,7 @@ module "premerge_cluster_us_central_resources" {
   runner_group_name                   = "llvm-premerge-cluster-us-central"
   linux_runners_namespace_name        = "llvm-premerge-linux-runners"
   windows_2022_runners_namespace_name = "llvm-premerge-windows-2022-runners"
-  github_arc_version                  = "0.11.0"
+  github_arc_version                  = "0.12.1"
   providers = {
     kubernetes = kubernetes.llvm-premerge-us-central
     helm       = helm.llvm-premerge-us-central
@@ -149,7 +149,7 @@ module "premerge_cluster_us_west_resources" {
   runner_group_name                   = "llvm-premerge-cluster-us-west"
   linux_runners_namespace_name        = "llvm-premerge-linux-runners"
   windows_2022_runners_namespace_name = "llvm-premerge-windows-2022-runners"
-  github_arc_version                  = "0.11.0"
+  github_arc_version                  = "0.12.1"
   providers = {
     kubernetes = kubernetes.llvm-premerge-us-west
     helm       = helm.llvm-premerge-us-west