UI: Change Update Available button text color to white

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

@@ -290,12 +290,12 @@
                     <Binding Path="UpdateAvailable" />
                 </MultiBinding>
             </StackPanel.IsVisible>
-            <Button Margin="0, 0, 5, 0"
+            <Button Margin="0, 0, 5, -2"
                     Command="{Binding UpdateCommand}"
                     Background="{DynamicResource SystemAccentColor}">
                 <TextBlock
                     Margin="-5"
-                    Foreground="Black"
+                    Foreground="{StaticResource SystemColorButtonTextColor}"
                     HorizontalAlignment="Right"
                     VerticalAlignment="Center"
                     Text="{ext:Locale UpdaterBackgroundStatusBarButtonText}" />