Revert Margin syntax change in XAML sample code

Co-authored-by: ayushjai19 <244442986+ayushjai19@users.noreply.github.com>

Author: Copilot

WinUIGallery/Samples/ControlPages/PipsPagerPage.xaml

@@ -42,7 +42,7 @@
     </FlipView>
     <PipsPager x:Name="FlipViewPipsPager"
         HorizontalAlignment="Center"
-        Margin="0,12,0,0"
+        Margin="0, 12, 0, 0"
         NumberOfPages="{x:Bind Pictures.Count}"
         SelectedPageIndex="{x:Bind Path=Gallery.SelectedIndex, Mode=TwoWay}" />
 </StackPanel>