Warning not harmful during MacOS build

[Tom3652]

Thanks for the package ! No real issue, a simple warning when i build my MacOS app but nothing harmful.

/Users/foxtom/.pub-cache/hosted/pub.dev/audio_session-0.2.2/macos/audio_session/Sources/audio_session/AudioSessionPlugin.m:14:5: warning: expression result unused [-Wunused-value]
   14 |     [[AudioSessionPlugin alloc] initWithRegistrar:registrar];
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 warning generated.