UI: Show Update Available button in the system accent color

src/Ryujinx/UI/Views/Main/MainStatusBarView.axaml

@@ -291,9 +291,11 @@
                 </MultiBinding>
             </StackPanel.IsVisible>
             <Button Margin="0, 0, 5, 0"
-                    Command="{Binding UpdateCommand}">
+                    Command="{Binding UpdateCommand}"
+                    Background="{DynamicResource SystemAccentColor}">
                 <TextBlock
                     Margin="-5"
+                    Foreground="Black"
                     HorizontalAlignment="Right"
                     VerticalAlignment="Center"
                     Text="{ext:Locale UpdaterBackgroundStatusBarButtonText}" />