## What changed?
If the group by key is returned as `[]byte`, convert it to string in
`CountWorkflowExecutions` and `CountCHASMExecutions`.
## Why?
The Go driver for MySQL returns `VARCHAR` columns as `[]byte`. This is
apparently not true of our other persistence backends.
## How did you test it?
- [x] built
- [x] added new functional test(s)
## Potential risks
Could break workflow visibility queries if this change is not correct.
Dan Davison
c3393ac92a