fix checkbox border not showing on fluent light theme.

src/Avalonia.Themes.Fluent/Accents/FluentControlResourcesLight.xaml

@@ -366,8 +366,8 @@
     <x:Double x:Key="AutoCompleteBoxIconFontSize">12</x:Double>
 
     <!-- Resources for CheckBox.xaml -->
-    <x:Double x:Key="CheckBoxBorderThemeThickness">1</x:Double>
-    <x:Double x:Key="CheckBoxCheckedStrokeThickness">0</x:Double>
+    <Thickness x:Key="CheckBoxBorderThemeThickness">1</Thickness>
+    <Thickness x:Key="CheckBoxCheckedStrokeThickness">0</Thickness>
     <StaticResource x:Key="CheckBoxForegroundUnchecked" ResourceKey="SystemControlForegroundBaseHighBrush" />
     <StaticResource x:Key="CheckBoxForegroundUncheckedPointerOver" ResourceKey="SystemControlForegroundBaseHighBrush" />
     <StaticResource x:Key="CheckBoxForegroundUncheckedPressed" ResourceKey="SystemControlForegroundBaseHighBrush" />