yuzu: Resolve C++20 deprecation warnings related to lambda captures

C++20 deprecates capturing the this pointer via the '=' capture.
Instead, we replace it or extend the capture specification.

src/core/hle/service/audio/audout_u.cpp

@@ -71,7 +71,7 @@ public:
 
         stream = audio_core.OpenStream(system.CoreTiming(), audio_params.sample_rate,
                                        audio_params.channel_count, std::move(unique_name),
-                                       [=]() { buffer_event.writable->Signal(); });
+                                       [this] { buffer_event.writable->Signal(); });
     }
 
 private: