Fix karma out-of-memory failures

What does this MR do?

Karma started running out of memory in EE after gitlab-org/gitlab-ee!7481 and this change was employed to fix it.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides