It's not really a problem. It either shows that your default vehicles_airport.bgl file is not original anymore, so the installer won't patch it, or it just mean it's missing, because it was removed after you initially installed GSX.
Since the GSX installer obviously made a backup before trying to patch it, that message is simply saying that is restoring from the backup.
If your file is not default, there's nothing else you can do, the file will not be patched (if you used 3rd party ground vehicles replacement sets)
If, instead, the file was missing, now that GSX has restored it from the backup, you might try running the GSX installer again to let the installer another chance to patch it.
The only reason to patch that file, is to remove the default pushback truck, so you won't see both at a parking. It's not usually a problem, since starting positions are usually different in GSX, it's just a cosmetic issue.