use fully deterministic concurrency for while-queued tests

Author: RalfJung

tests/fail-dep/concurrency/libc_pthread_mutex_read_while_queued.rs

@@ -1,5 +1,5 @@
 //@ignore-target: windows # No pthreads on Windows
-//@compile-flags: -Zmiri-fixed-schedule
+//@compile-flags: -Zmiri-deterministic-concurrency
 
 use std::cell::UnsafeCell;
 use std::sync::atomic::*;

tests/fail-dep/concurrency/libc_pthread_mutex_write_while_queued.rs

@@ -1,5 +1,5 @@
 //@ignore-target: windows # No pthreads on Windows
-//@compile-flags: -Zmiri-fixed-schedule
+//@compile-flags: -Zmiri-deterministic-concurrency
 
 use std::cell::UnsafeCell;
 use std::sync::atomic::*;