fix: configure automerge package manager (#674)

Author: peternhale

.github/workflows/automerge.yml

@@ -7,4 +7,7 @@ on:
 jobs:
   automerge:
     uses: salesforcecli/github-workflows/.github/workflows/automerge.yml@main
+    with:
+      package-manager: yarn
+      cache-dependency-path: yarn.lock
     secrets: inherit