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/neighbor/plugins/SmbclientNeighborPlugin.cxx

@@ -99,7 +99,7 @@ void
 SmbclientNeighborExplorer::Close() noexcept
 {
 	{
-		const std::lock_guard<Mutex> lock(mutex);
+		const std::scoped_lock<Mutex> lock(mutex);
 		quit = true;
 		cond.notify_one();
 	}
@@ -110,7 +110,7 @@ SmbclientNeighborExplorer::Close() noexcept
 NeighborExplorer::List
 SmbclientNeighborExplorer::GetList() const noexcept
 {
-	const std::lock_guard<Mutex> protect(mutex);
+	const std::scoped_lock<Mutex> protect(mutex);
 	return list;
 }
 

src/neighbor/plugins/UdisksNeighborPlugin.cxx

@@ -175,7 +175,7 @@ UdisksNeighborExplorer::Close() noexcept
 NeighborExplorer::List
 UdisksNeighborExplorer::GetList() const noexcept
 {
-	const std::lock_guard<Mutex> lock(mutex);
+	const std::scoped_lock<Mutex> lock(mutex);
 
 	NeighborExplorer::List result;
 
@@ -192,7 +192,7 @@ UdisksNeighborExplorer::Insert(UDisks2::Object &&o) noexcept
 	const NeighborInfo info = ToNeighborInfo(o);
 
 	{
-		const std::lock_guard<Mutex> protect(mutex);
+		const std::scoped_lock<Mutex> protect(mutex);
 		auto i = by_uri.emplace(o.GetUri(), info);
 		if (!i.second)
 			i.first->second = info;