Skip TestConcurrentWatchBreak.py on Darwin arm64

This test depends on multiple threads with one of them
hitting a watchpoint at the same time as a breakpoint, and
can fail because of the way arm64 watchpoints are handled.
I added skips to most of these via

```
commit bef4da4a
Author: Jason Molenda <jason@molenda.com>
Date:   Wed May 25 16:05:16 2022 -0700

    Skip testing of watchpoint hit-count/ignore-count on multithreaded
```

but missed that this test is susceptable to the same issue.