Switch release train runners back to SMS

Recent connectivity issues between Leafcloud and SMS have been impacting
CI. This change centralises the nightly sync CI on Leafcloud

Author: Alex-Welsh

.github/workflows/package-sync-nightly.yml

@@ -9,7 +9,7 @@ env:
 jobs:
   sync-matrix-build:
     name: Build package matrix of package repo sync jobs
-    runs-on: arc-release-train-runner-sms
+    runs-on: arc-release-train-runner
     outputs:
       matrix: ${{ steps.matrix-build.outputs.matrix }}
     steps: