fix: update automerge job to run for dependabot user

Signed-off-by: Vinayak Kulkarni <19776877+vinayakkulkarni@users.noreply.github.com>

.github/workflows/automerger.yml

@@ -1,11 +1,15 @@
 name: 'Auto Merge PRs'
 
 on:
-  workflow_call:
+  pull_request:
+    branches:
+      - master
 
 jobs:
   automerge:
     runs-on: ubuntu-latest
+    if: >
+      github.event_name == 'pull_request' && github.event.pull_request.user.login == 'dependabot[bot]'
     permissions:
       pull-requests: write
       contents: write