try modulo

Author: boomanaiden154

.github/workflows/premerge.yaml

@@ -29,7 +29,7 @@ jobs:
         github.repository_owner == 'llvm' &&
         (github.event_name != 'pull_request' || github.event.action != 'closed')
     runs-on:
-      group: llvm-premerge-cluster-us-west
+      group: ${{ github.run_id % 2 == 0 && 'llvm-premerge-cluster-us-west' || 'llvm-premerge-cluster-us-central' }}
       labels: llvm-premerge-linux-runners
     steps:
       - name: Checkout LLVM