Fix mono test app compilation.
Fix mono test app compilation.

MrDaedra/Avalonia,jkoritzinsky/Avalonia,bbqchickenrobot/Perspex,AvaloniaUI/Avalonia,DavidKarlas/Perspex,SuperJMN/Avalonia,susloparovdenis/Perspex,wieslawsoltes/Perspex,akrisiun/Perspex,danwalmsley/Perspex,grokys/Perspex,AvaloniaUI/Avalonia,jkoritzinsky/Avalonia,SuperJMN/Avalonia,jkoritzinsky/Avalonia,SuperJMN/Avalonia,tshcherban/Perspex,jkoritzinsky/Perspex,wieslawsoltes/Perspex,MrDaedra/Avalonia,susloparovdenis/Avalonia,wieslawsoltes/Perspex,susloparovdenis/Avalonia,punker76/Perspex,AvaloniaUI/Avalonia,wieslawsoltes/Perspex,jkoritzinsky/Avalonia,SuperJMN/Avalonia,jkoritzinsky/Avalonia,wieslawsoltes/Perspex,sagamors/Perspex,AvaloniaUI/Avalonia,AvaloniaUI/Avalonia,kekekeks/Perspex,jazzay/Perspex,SuperJMN/Avalonia,jkoritzinsky/Avalonia,OronDF343/Avalonia,wieslawsoltes/Perspex,jkoritzinsky/Avalonia,grokys/Perspex,AvaloniaUI/Avalonia,SuperJMN/Avalonia,kekekeks/Perspex,susloparovdenis/Perspex,SuperJMN/Avalonia,wieslawsoltes/Perspex,AvaloniaUI/Avalonia,Perspex/Perspex,ncarrillo/Perspex,Perspex/Perspex,OronDF343/Avalonia