fixes typo on mac icon fix

[brunocastello]

Summary

This fixes a typo on a mac icon fix submitted by lemondrops.
The original code uses
#ifndef Q_OS_APPLE
instead of
#ifndef __APPLE__

After changing this line, the correct icon appears on MacOS Dock, for both app window and settings window.

Checklist

• Closes Don't set the application icon in qt_main.c on Mac #3973
• I have discussed this with core contributors already
• This pull request requires changes to the ROM set
  • I have opened a roms pull request - https://github.com/86Box/roms/pull/changeme/

References

OBattler

[lemondrops]

Are you sure? They should evaluate to the same thing.
Nevermind, my bad, it should've actually been Q_OS_MACOS instead.