Permanently enables enforce_abilities_check_for_dependency_proxy

What does this MR do and why?

Dependency proxy authentication now enforces scope checks

https://docs.gitlab.com/update/deprecations/#dependency-proxy-token-scope-enforcement

Changelog: changed

References

• Related to issue #426887 (closed)
• Deprecation notice: https://docs.gitlab.com/update/deprecations/#dependency-proxy-token-scope-enforcement
• Rollout issue: #521193 (closed)

How to set up and validate locally

1. Have a group and a user with access to that group ready, e.g. group 33 (Flightjs) and root user on GDK
2. Personal access tokens, group access tokens, and group deploy tokens with the required scopes - api or read_registry + write_registry should be able to login
3. Personal access tokens, group access tokens and group deploy tokens without the required scopes - e.g. read_registry only - should get a HTTP 403 response

MR acceptance checklist

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