Add package write permission to docker-image job

[ranisalt]

Pull Request Prelude

• [x] I have followed proper The Forgotten Server code styling.
• [x] I have read and understood the contribution guidelines before making this PR.
• [x] I am aware that this PR may be closed if the above-mentioned criteria are not fulfilled.

Changes Proposed

Issues addressed: after #4702 we learned that the GITHUB_TOKEN is configured in restricted mode, which removes the access to publish packages, Docker images included. Since changing the token access is not a possibility, we need to granularly enable the permission for this job.