Fix maintainer-approval to use custom runner group

The databricks org has an IP allow-list that blocks GitHub public
runners from making API calls. Use the same custom runner group as
the other workflows in this repo.

Author: simonfaltum

.github/workflows/maintainer-approval.yml

@@ -11,7 +11,9 @@ defaults:
 
 jobs:
   check:
-    runs-on: ubuntu-latest
+    runs-on:
+      group: databricks-deco-testing-runner-group
+      labels: ubuntu-latest-deco
     timeout-minutes: 5
     permissions:
       pull-requests: read