GitLab: Project Milestones Disclosed Via Groups When the Victim disabled milestones access in project settings

##Reproduction steps:

Create a public group and public project.

Go to public project settings and disable the project settings to members only.

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If the attacker visits milestones via projects then may see 404 not found page.

https://gitlab.com/victim-waka-waka/test-group-for-sharing/-/milestones/1

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But the attacker will view the project mile stones via groups.

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Impact

Attacker will view the project milestones which are disabled by the admin in project settings.