Switch to depot runners

Author: tstellar

.github/workflows/premerge.yaml

@@ -31,11 +31,11 @@ jobs:
     strategy:
       matrix:
         runs-on:
-          - ubuntu-24.04
+          - depot-ubuntu-24.04-arm-4
           - llvm-premerge-linux-runners
     runs-on: ${{ matrix.runs-on }}
     container:
-      image: ${{ (startsWith(matrix.runs-on, 'ubuntu-24.04') && format('ghcr.io/{0}/ci-ubuntu-24.04',github.repository_owner) ) || null }}
+      image: ${{ (startsWith(matrix.runs-on, 'depot-ubuntu-24.04-arm-16') && format('ghcr.io/{0}/arm64v8/ci-ubuntu-24.04',github.repository_owner) ) || null }}
     defaults:
       run:
         # The run step defaults to using sh as the shell when running in a