Allow checking interrupts when VM lock held

It was too restrictive to disallow this case, because we can raise a
ruby error while holding the VM lock, which calls initialize on the
error object, which can enter the interrupt checks. So intead, we
just don't switch to another thread if the VM lock is held.

Author: luke-gruber

thread.c

@@ -2596,7 +2596,6 @@ rb_threadptr_execute_interrupts(rb_thread_t *th, int blocking_timing)
     int ret = FALSE;
 
     VM_ASSERT(GET_THREAD() == th);
-    ASSERT_vm_unlocking();
 
     if (th->ec->raised_flag) return ret;
 
@@ -2677,7 +2676,7 @@ rb_threadptr_execute_interrupts(rb_thread_t *th, int blocking_timing)
             rb_threadptr_to_kill(th);
         }
 
-        if (timer_interrupt) {
+        if (timer_interrupt && th->vm->ractor.sync.lock_owner != th->ractor) {
             uint32_t limits_us = thread_default_quantum_ms * 1000;
 
             if (th->priority > 0)