Update dependabot-prs.yml

Author: CharlieTLe

.github/workflows/dependabot-prs.yml

@@ -1,14 +1,17 @@
 # Copyright The OpenTelemetry Authors
 # SPDX-License-Identifier: Apache-2.0
 name: Dependabot auto-merge
-on: pull_request
+on:
+  pull_request:
+      branches: [ main ]
 permissions:
   pull-requests: write
   contents: write
 jobs:
   dependabot:
     runs-on: ubuntu-latest
     if: github.event.pull_request.user.login == 'dependabot[bot]' && github.repository == 'charlietle/opentelemetry-demo'
+    needs: [build_images, markdownlint, yamllint, misspell, markdownlinkcheck, sanity, checklicense]
     steps:
       - name: Dependabot metadata
         id: dependabot-metadata