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>

test/run_input.cxx

@@ -223,14 +223,14 @@ public:
 
 	/* virtual methods from RemoteTagHandler */
 	void OnRemoteTag(Tag &&_tag) noexcept override {
-		const std::lock_guard<Mutex> lock(mutex);
+		const std::scoped_lock<Mutex> lock(mutex);
 		tag = std::move(_tag);
 		done = true;
 		cond.notify_all();
 	}
 
 	void OnRemoteTagError(std::exception_ptr e) noexcept override {
-		const std::lock_guard<Mutex> lock(mutex);
+		const std::scoped_lock<Mutex> lock(mutex);
 		error = std::move(e);
 		done = true;
 		cond.notify_all();