Use std::bind in QtConcurrent::run() to fix compile with Qt 6

src/playlist/songloaderinserter.cpp

@@ -83,7 +83,7 @@ void SongLoaderInserter::Load(Playlist *destination, int row, bool play_now, boo
     deleteLater();
   }
   else {
-    QtConcurrent::run(this, &SongLoaderInserter::AsyncLoad);
+    (void)QtConcurrent::run([=]{ AsyncLoad(); });
   }
 }