Use different FF in shared runners limit check

What does this MR do?

In the !27792 (merged), we have a minor issue with our two feature flags.

The idea was to enable the first flag (ci_minutes_track_for_public_projects) and start accumulating the minutes for public projects without putting any restrictions/limiting (so we could test the numbers and also the pressure on background jobs if needed) while the second feature flag (ci_minutes_enforce_quota_for_public_projects) would force the limits.

The issue: UpdateBuildMinutesService currently does return unless build.shared_runners_minutes_limit_enabled? which is implemented as ::Feature.enabled?(:ci_minutes_enforce_quota_for_public_projects) (second feature flag).

So, with the current implementation, enabling just the first feature flag will not accumulate minutes for public. We need them both to even track the minutes which is not what we want. So we're fixing it.

We update implementations of def shared_runners_minutes_limit_enabled? in project and build to rely on the ci_minutes_track_for_public_projects for the given namespace instead ci_minutes_enforce_quota_for_public_projects.

The only minor downside of such change that we won't change :with_shared_runners_limit_enabled scope (it would rely on the second flag), which is slightly inconsistent, but I think this should be fine.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• [-] Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

N/A

Relates to #210570 (closed)