Merge pull request godotengine#116531 from lawnjelly/mutex_lock_no_discard

[3.x] Mark MutexLock as `NO_DISCARD` to prevent misuse.

Author: lawnjelly

core/os/mutex.h

@@ -59,7 +59,7 @@ class MutexImpl {
 
 // This is written this way instead of being a template to overcome a limitation of C++ pre-17
 // that would require MutexLock to be used like this: MutexLock<Mutex> lock;
-class MutexLock {
+class _NO_DISCARD_CLASS_ MutexLock {
 	union {
 		std::recursive_mutex *recursive_mutex;
 		std::mutex *mutex;
@@ -107,7 +107,7 @@ class MutexImpl {
 	_ALWAYS_INLINE_ Error try_lock() const { return OK; }
 };
 
-class MutexLock {
+class _NO_DISCARD_CLASS_ MutexLock {
 public:
 	explicit MutexLock(const MutexImpl<FakeMutex> &p_mutex) {}
 };