Move expensive test jobs to new high-cpu runners

What does this MR do?

Moves some compute expensive tests to new high-cpu runners as discussed in gitlab-com/infrastructure#2046.

Are there points in the code the reviewer needs to double check?

To new runners I've moved:

• all rspec jobs,
• all spinach jobs,
• gitlab:assets:compile job,
• setup-test-env job.

Is there anything else that is compute expensive and we'd like it to be executed on high-cpu?

Why was this MR needed?

Please read gitlab-com/infrastructure#2046 for a reference.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes gitlab-com/infrastructure#2046