[mono][tests] Fix deadlock in pinvoke detach test (#88855)

Without holding the condition mutex, the test is starting a new thread that is signaling us back. This means that the new thread could fail to signal us back, because there could be no waiters and the test would deadlock.

src/tests/Interop/MonoAPI/Native/mono-embedding-api-test/mono-embedding-api-test.c

@@ -1069,13 +1069,14 @@ mono_test_attach_invoke_block_foreign_thread (const char *assm_name, const char
 	pthread_mutex_init (&nm->deadlock_mutex, NULL);
 
 	pthread_mutex_lock (&nm->deadlock_mutex); // lock the mutex and never unlock it.
+
+	pthread_mutex_lock (&nm->coord_mutex);
 	pthread_t t;
 	int res = pthread_create (&t, NULL, invoke_block_foreign_thread, (void*)nm);
 	assert (res == 0);
 	/* wait for the foreign thread to finish calling the runtime before
 	 * detaching it and returning
 	 */
-	pthread_mutex_lock (&nm->coord_mutex);
 	pthread_cond_wait (&nm->coord_cond, &nm->coord_mutex);
 	pthread_mutex_unlock (&nm->coord_mutex);
 	pthread_detach (t);