Apply “draft trick” to `process-dependabot-reusable.yaml`

This change applies the “draft trick” to `process-dependabot-reusable.yaml`: instead of enabling “auto-merge” on the PR, it puts it into draft mode. This allows the removal of a PAT at the cost of two additional actions for maintainers that need to:

1. Approve the PR,
2. Put it into “Ready for review” state. If workflows are listening to `ready_for_review`, they will start,
3. Enable “auto-merge” on the PR.