Fix typo in NavigationView Sample 5 (#1567)

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## Description
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This fixes a typo in the XAML snippets of NavigationView sample 5

## Motivation and Context
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This change makes the sample working

## Types of changes
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the boxes that apply: -->
- [x] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [ ] Breaking change (fix or feature that would cause existing
functionality to change)

WinUIGallery/ControlPagesSampleCode/NavigationView/NavigationViewSample5.txt

@@ -5,7 +5,7 @@
 <local:MenuItemTemplateSelector x:Key="selector"> 
     <local:MenuItemTemplateSelector.ItemTemplate> 
         <DataTemplate x:DataType="local:Category" > 
-            <muxcontrols:NavigationViewItem Content="{x:Bind Name}" TooltipService.ToolTip="{x:Bind Tooltip}"> 
+            <muxcontrols:NavigationViewItem Content="{x:Bind Name}" ToolTipService.ToolTip="{x:Bind Tooltip}"> 
                 <muxcontrols:NavigationViewItem.Icon> 
                     <SymbolIcon Symbol="{x:Bind Glyph}" /> 
                 </muxcontrols:NavigationViewItem.Icon> 

WinUIGallery/ControlPagesSampleCode/NavigationView/NavigationViewSample5_xaml.txt

@@ -5,7 +5,7 @@
 <local:MenuItemTemplateSelector x:Key="selector"> 
     <local:MenuItemTemplateSelector.ItemTemplate> 
         <DataTemplate x:DataType="local:Category" > 
-            <NavigationViewItem Content="{x:Bind Name}" TooltipService.ToolTip="{x:Bind Tooltip}"> 
+            <NavigationViewItem Content="{x:Bind Name}" ToolTipService.ToolTip="{x:Bind Tooltip}"> 
                 <NavigationViewItem.Icon> 
                     <SymbolIcon Symbol="{x:Bind Glyph}" /> 
                 </NavigationViewItem.Icon>