[TSan] Relax pthread introspection-based test

Thread create/destroy events are not guaranteed to belivered on the
parent thread, e.g., output from a CI job:
```
5: THREAD_CREATE 0x7e8000104000, self: 0x1102ebdc0, name: n/a
6: THREAD_START 0x7e8000104000, self: 0x7e8000104000, name: n/a
7: Hello from pthread
8: THREAD_TERMINATE 0x7e8000104000, self: 0x7e8000104000, name: child thread
9: THREAD_DESTROY 0x7e8000104000, self: 0x7e8000104000, name: child thread
```
Here, THREAD_DESTROY is delivered on the thread being destroyed.

rdar://92679941