ci: update token used by Dependabot auto-merge

Author: matchai

.github/workflows/merge-dependabot.yml

@@ -9,6 +9,6 @@ jobs:
     steps:
       - uses: akheron/dependabot-cron-action@b44d8e19e4f49eede254d9884e3f0e7712d431ba
         with:
-          token: ${{ secrets.GITHUB_TOKEN }}
+          token: ${{ secrets.DEPENDABOT_GITHUB_API_TOKEN }}
           auto-merge: "minor"
           merge-method: "squash"