Respect namespaces with unlimited minutes

What does this MR do?

In incident 5392 we found that the gitlab security project was marked as running out of minutes.

All internal gitlab owned projects typically have unlimited minutes by way of namespace.shared_runners_minutes_limit == 0.

When this MR was introduced it broke skipping calculations on namespaces with 'unlimited minutes' in the track live consumption service. We introduced another check to return the same kind of error response to skip cost factor calculations.

Screenshots or Screencasts (strongly suggested)

How to setup and validate locally (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)