[Obs AI Assistant] Fix conversation test in serverless MKI

[neptunian]

The test suite, when creating a conversation with the write user, fails in MKI. It compares the response of a conversation with a specific user, which can change from local to MKI which generates numbers as a username. This could potentially be controlled using cookie_auth to set the username. Otherwise remove checking the body for the exact username or get it ahead of time if possible.

[neptunian]

change made in #192219 to not test against the user name. I think in MKI the name could be different numbers each time an environment is created.