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/event/Loop.cxx

@@ -323,7 +323,7 @@ EventLoop::Run() noexcept
 		/* try to handle DeferEvents without WakeFD
 		   overhead */
 		{
-			const std::lock_guard<Mutex> lock(mutex);
+			const std::scoped_lock<Mutex> lock(mutex);
 			HandleInject();
 #endif
 
@@ -346,7 +346,7 @@ EventLoop::Run() noexcept
 
 #ifdef HAVE_THREADED_EVENT_LOOP
 		{
-			const std::lock_guard<Mutex> lock(mutex);
+			const std::scoped_lock<Mutex> lock(mutex);
 			busy = true;
 		}
 #endif
@@ -378,7 +378,7 @@ EventLoop::AddInject(InjectEvent &d) noexcept
 	bool must_wake;
 
 	{
-		const std::lock_guard<Mutex> lock(mutex);
+		const std::scoped_lock<Mutex> lock(mutex);
 		if (d.IsPending())
 			return;
 
@@ -397,7 +397,7 @@ EventLoop::AddInject(InjectEvent &d) noexcept
 void
 EventLoop::RemoveInject(InjectEvent &d) noexcept
 {
-	const std::lock_guard<Mutex> protect(mutex);
+	const std::scoped_lock<Mutex> protect(mutex);
 
 	if (d.IsPending())
 		inject.erase(inject.iterator_to(d));
@@ -424,7 +424,7 @@ EventLoop::OnSocketReady([[maybe_unused]] unsigned flags) noexcept
 
 	wake_fd.Read();
 
-	const std::lock_guard<Mutex> lock(mutex);
+	const std::scoped_lock<Mutex> lock(mutex);
 	HandleInject();
 }