race condition in waitany test

Tests in #53341 are prone to a race condition if they take more than 0.001 seconds to execute, as seen here:
```
throw=true: Test Failed at /home/vtjnash/julia/test/threads_exec.jl:1237
  Expression: begin
    #= /home/vtjnash/julia/test/threads_exec.jl:1238 =#
    waitany(convert_tasks(tasks_type, tasks); throw = true)
end
    Expected: CompositeException
  No exception thrown
```