tests: posix: common: add a small delay in pthread_descriptor_leak

Technically speaking, there should be a synchronization to ensure
that a spawned thread has started before `pthread_join()` is
called.

However, since we're recycling an existing no-op thread, just add
a small delay.

A separate test will be used to demonstrate stressing
`pthread_create()` and `pthread_join()` which will use a
synchronization primitive.

Signed-off-by: Christopher Friedt <[email protected]>

Author: Christopher Friedt

tests/posix/common/src/pthread.c

@@ -594,6 +594,8 @@ ZTEST(posix_apis, test_pthread_descriptor_leak)
 	for (size_t i = 0; i < CONFIG_MAX_PTHREAD_COUNT * 2; ++i) {
 		zassert_ok(pthread_create(&pthread1, &attr, create_thread1, NULL),
 			   "unable to create thread %zu", i);
+		/* Small delay to prevent joining before the thread has been spawned */
+		k_msleep(100);
 		zassert_ok(pthread_join(pthread1, NULL), "unable to join thread %zu", i);
 	}
 }