treewide: replace lock_guard with scoped_lock

SonarLint reports the latter to be better:

std::scoped_lock basically provides the same feature as std::lock_guard,
but is more generic: It can lock several mutexes at the same time, with a
deadlock prevention mechanism (see {rule:cpp:S5524}). The equivalent code
to perform simultaneous locking with std::lock_guard is significantly more
complex. Therefore, it is simpler to use std::scoped_lock all the time,
even when locking only one mutex (there will be no performance impact).

Signed-off-by: Rosen Penev <rosenp@gmail.com>

src/storage/plugins/NfsStorage.cxx

@@ -139,7 +139,7 @@ private:
 	void SetState(State _state) noexcept {
 		assert(GetEventLoop().IsInside());
 
-		const std::lock_guard<Mutex> protect(mutex);
+		const std::scoped_lock<Mutex> protect(mutex);
 		state = _state;
 		cond.notify_all();
 	}
@@ -147,7 +147,7 @@ private:
 	void SetState(State _state, std::exception_ptr &&e) noexcept {
 		assert(GetEventLoop().IsInside());
 
-		const std::lock_guard<Mutex> protect(mutex);
+		const std::scoped_lock<Mutex> protect(mutex);
 		state = _state;
 		last_exception = std::move(e);
 		cond.notify_all();