use shared static mutex in pthread_mutex_lock test

Agent-Logs-Url: https://github.com/acl-dev/open-coroutine/sessions/a4199b83-4d02-43f6-aa5a-f79a5303135a

Co-authored-by: loongs-zhang <38336731+loongs-zhang@users.noreply.github.com>

Author: Copilot

core/tests/scheduler.rs

@@ -136,21 +136,21 @@ fn scheduler_pthread_mutex_lock() -> std::io::Result<()> {
     use std::sync::atomic::{AtomicUsize, Ordering};
 
     static COUNTER: AtomicUsize = AtomicUsize::new(0);
+    static mut MUTEX: libc::pthread_mutex_t = libc::PTHREAD_MUTEX_INITIALIZER;
 
     let mut scheduler = Scheduler::default();
     for _ in 0..3 {
         _ = scheduler.submit_co(
             |_, _| {
-                let mut mutex = libc::PTHREAD_MUTEX_INITIALIZER;
                 let r = open_coroutine_core::syscall::pthread_mutex_lock(
                     None,
-                    std::ptr::addr_of_mut!(mutex),
+                    std::ptr::addr_of_mut!(MUTEX),
                 );
                 assert_eq!(0, r, "pthread_mutex_lock failed with {r}");
                 COUNTER.fetch_add(1, Ordering::SeqCst);
                 let r = open_coroutine_core::syscall::pthread_mutex_unlock(
                     None,
-                    std::ptr::addr_of_mut!(mutex),
+                    std::ptr::addr_of_mut!(MUTEX),
                 );
                 assert_eq!(0, r, "pthread_mutex_unlock failed with {r}");
                 None