Resolve "Follow-up from "Enable multiple queries per Prometheus graph""

What does this MR do?

Adds the missing computed prop test for strokeDashArray

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by Frontend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together
• Internationalization required/considered

What are the relevant issue numbers?

Closes #39861 (closed)