fix: oversight in SoftwareMixer loop

Signed-off-by: Maximilien Noal <noal.maximilien@gmail.com>

src/Spice86.Core/Emulator/Devices/Sound/SoftwareMixer.cs

@@ -42,7 +42,7 @@ internal int Render(Span<float> data, SoundChannel channel) {
         float finalVolumeFactor = volumeFactor * (1 + separation);
 
         Span<float> target = stackalloc float[data.Length];
-        for (int i = 0; i < data.Length; i++) {
+        for (int i = 0; i < data.Length; i += 2) {
             // Apply volume and separation to left channel
             target[i] = data[i] * finalVolumeFactor;
             // Ensure we don't go out of range