run-cats: Refactor task to remove unnecessary copy to GOPATH

[ctlong]

What is this change about?

Refactors run-cats to not put CATs repo in the GOPATH, which is unnecessary.

Please provide contextual information.

None

Please check all that apply for this PR:

• [ ] introduces a new task
• [x] changes an existing task
• [ ] changes the Dockerfile
• [ ] introduces a breaking change (other users will need to make manual changes when this is released)

Did you update the README as appropriate for this change?

• [ ] YES
• [x] N/A

What is the level of urgency for publishing this change?

• [ ] Urgent - unblocks current or future work
• [x] Slightly Less than Urgent

Tag your pair, your PM, and/or team!

None