qthread::testQThread manual test breakpoint does not behave as expected on macOS

Following the instruction at https://wiki.qt.io/Qt_Creator_ManualTests_DebuggerLldb ->
Test a breakpoint in a QThread

There are 16 threads created, but the number of times the breakpoint is hit is less than half the threads.

hjk says it most likely happens due to insertBreakpoint() happening after runEngine().