Update ListView sample code to match used resources (#1383)

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## Description
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The brushes used for the messaging sample were out of date which this PR
addresses.
## Motivation and Context
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## How Has This Been Tested?
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## Types of changes
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the boxes that apply: -->
- [ ] 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/ControlPages/ListViewPage.xaml

@@ -337,9 +337,9 @@ source code for the WinUI Gallery. -->
 sent or received, and those values are bound in the DataTemplate.-->
 <DataTemplate x:Key="MessageViewTemplate" x:DataType="local1:Message">
     <Grid Height="Auto" Margin="4" HorizontalAlignment="{x:Bind MsgAlignment}">
-        <StackPanel MinHeight="75" Width="350" Padding="10, 0, 0, 10" Background="{x:Bind BgColor}" CornerRadius="{StaticResource ControlCornerRadius}">
-            <TextBlock Text="{x:Bind MsgText}" Padding="0, 10, 0, 0" FontSize="20" Foreground="{ThemeResource SystemControlForegroundAltHighBrush}"/>
-            <TextBlock Text="{x:Bind MsgDateTime}" Padding="0, 0, 0, 10" FontSize="15" Foreground="{ThemeResource SystemControlForegroundAltMediumHighBrush}"/>
+        <StackPanel MinHeight="75" Width="350" Padding="10, 0, 0, 10" Background="{ThemeResource SystemColorHighlightColor}" CornerRadius="{StaticResource ControlCornerRadius}">
+            <TextBlock Text="{x:Bind MsgText}" Padding="0, 10, 0, 0" FontSize="20" Foreground="{ThemeResource SystemColorHighlightTextColor}"/>
+            <TextBlock Text="{x:Bind MsgDateTime}" Padding="0, 0, 0, 10" FontSize="15" Foreground="{ThemeResource SystemColorHighlightTextColor}"/>
         </StackPanel>
     </Grid>
 </DataTemplate>