MDEV-27088: lf unit tests - cycles insufficient

Per bug report, cycles was woefully insufficient to
detect any implementation error.

unittest/mysys/thr_template.c

@@ -60,7 +60,7 @@ int main(int argc __attribute__((unused)), char **argv)
 
   pthread_mutex_init(&mutex, 0);
 
-#define CYCLES 3000
+#define CYCLES 30000
 #define THREADS 30
 
   diag("N CPUs: %d, atomic ops: %s", my_getncpus(), MY_ATOMIC_MODE);