Update WinUIGallery/Samples/SampleCode/SystemBackdropHost/SystemBackdropHostMica_xaml.txt

Co-authored-by: Niels Laute <niels.laute@live.nl>

Author: rashmi-thakurr

WinUIGallery/Samples/SampleCode/SystemBackdropHost/SystemBackdropHostMica_xaml.txt

@@ -4,5 +4,5 @@
             <MicaBackdrop Kind="Base" />
         </SystemBackdropHost.SystemBackdrop>
     </SystemBackdropHost>
-    <Button Content="Click Me" HorizontalAlignment="Center" VerticalAlignment="Center"/>
+    <Button Content="Button" HorizontalAlignment="Center" VerticalAlignment="Center"/>
 </Grid>