Fix EnvironmentNamesFinder for private projects

What does this MR do?

When using EnvironmentNamesFinder for a group, environments for private projects are only supposed to be visible to users with reporter access or greater. Previously also guests would be able to see environment names.

This fixes #270939 (closed), and builds upon !45551 (merged).

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry Feature is not yet released
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content