`register-dockerfile`: `PRIVATE_TOKEN` is no longer needed since `ci_job_token_scope` is enabled
The last paragraph in register-dockerfile/README.md
should be updated:
This job requires the CI variable `PRIVATE_TOKEN` to be set to an [access token](https://docs.gitlab.com/ee/user/project/settings/project_access_tokens.html#create-a-project-access-token) with `api` permissions, to enable the script to access repository tags (access repository tags for CI job token is behind the `ci_job_token_scope` feature flag).