fix syntax

Author: boomanaiden154

.github/workflows/premerge.yaml

@@ -30,7 +30,7 @@ jobs:
         (github.event_name != 'pull_request' || github.event.action != 'closed')
     runs-on:
       group: llvm-premerge-cluster-us-west
-      label: llvm-premerge-linux-runners
+      labels: llvm-premerge-linux-runners
     steps:
       - name: Checkout LLVM
         uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0