Use a token dedicated to Dependabot

The automatic token is not available to Dependabot.

Author: cbandy

.github/dependabot.yml

@@ -16,13 +16,12 @@ version: 2
 registries:
   # Authenticate to GitHub for higher API rate limits
   # https://docs.github.com/en/rest/using-the-rest-api/rate-limits-for-the-rest-api
-  # https://docs.github.com/en/actions/how-tos/security-for-github-actions/security-guides/automatic-token-authentication
   # https://docs.github.com/en/code-security/dependabot/working-with-dependabot/configuring-access-to-private-registries-for-dependabot#git
   github:
     type: git
     url: https://github.com
     username: x-access-token
-    password: ${{ secrets.GITHUB_TOKEN }}
+    password: ${{ secrets.DEPENDABOT_TOKEN }}
 
 updates:
   - package-ecosystem: github-actions