winpthreads: tests: do not use `pthread_mutex_lock` in *-timedlock mutex tests

These tests used `pthread_mutex_lock` to initially lock the mutex.
Use `pthread_mutex_timedlock` instead.

Signed-off-by: Kirill Makurin <maiddaisuki@outlook.com>
Signed-off-by: LIU Hao <lh_mouse@126.com>