Added tests for the error handling in AiGenie

What does this MR do and why?

The MR simply adds the test for error handling in GraphQL subscription for AiGenie component

Screenshots or screen recordings

No visual changes

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #406783