Fix typo in ContentIsland page (#1890)

## Description
Changed the header of the ContentIsland control example from "A basic
content dialog with content." to "A basic content island with content.".

## Motivation and Context
This fix prevents confusion from users thinking they opened the
ContentDialog page when they actually opened the ContentIsland page.

## Screenshots:
![Screenshot 2025-05-26
205122](https://github.com/user-attachments/assets/339d43fa-141f-400a-8af5-b499597bcb30)
![Screenshot 2025-05-26
205048](https://github.com/user-attachments/assets/a4efac63-5a13-473a-94bd-6aa0b6de03f2)

## Types of changes
- [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)

Author: MGGSK

WinUIGallery/Samples/ControlPages/ContentIslandPage.xaml

@@ -24,7 +24,7 @@
                 </Style.Setters>
             </Style>
         </Grid.Resources>
-        <controls:ControlExample HeaderText="A basic content dialog with content." SourceCodeVisibility="Collapsed">
+        <controls:ControlExample HeaderText="A basic content island with content." SourceCodeVisibility="Collapsed">
             <controls:ControlExample.Example>
                 <Grid RowSpacing="8">
                     <Grid.RowDefinitions>