…ce testing

Fixes #23630

**Description**

Three event counters don't get updated when the async API is used (as opposed to the sync one). An additional event counter is incorrectly updated, and so show wrong results.

**Customer Impact**

Our newly-introduced event counters show incorrect data which does not take into account async calls.

**How found**

Customer reported an issue on 5.0.0 with one counter, the rest discovered via due diligence.

**Test coverage**

Test coverage added after investigation and discussion of the best way to do it. We settled on using reflection to access the counters and then configuring the tests to not run in parallel. These tests are both for detecting regressions, and so that going forward we can test new event counters to avoid mistakes like this in the future.

**Regression?**

No, event counters are new in 5.0.0.

**Risk**

Very low, add missing counter updates which are already in place and working for the sync versions, and move the location of another counter update. Only affects the new event counters feature.