tests: posix: semaphores: reduce execution time by 5s

There is no reason to use a 5s wait time in tests. This can add up quite
significantly across multiple platforms that execute in real-time under
qemu (or even just on real hardware).

Speedup observed with qemu_cortex_a53/qemu_cortex_a53/smp

Before:
```
START - test_named_semaphore
 PASS - test_named_semaphore in 5.688 seconds
```

After:
```
START - test_named_semaphore
 PASS - test_named_semaphore in 0.783 seconds
```

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>