Consider moving away from Mock due to race conditions

[HaoK]

Followup to #27032 (comment)

Yup, there's a race condition in CastleCore which shows up once in a blue moon.

[captainsafia]

We discussed this during triage. In order to effectively remove these issues in our tests, we would need to remove all instances of Mock in our test suite, which is an expensive task.

An alternative consideration is to fix this issue (castleproject/Core#193) in CastleCore, but it's difficult to create a reliable repro for this situation.

Considering this doesn't happen frequently and it's difficult to fix, we'll live with it for now and leverage retries to work around it.

[captainsafia]

cc: @BrennanConroy We discussed this during triage and figured you'd like to know what we discussed.

[ghost]

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.