Added a UI test (dotnet#20273)

Author: kubaflo

src/Controls/samples/Controls.Sample.UITests/Issues/Issue20273.xaml

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+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue20273">
+
+        <ContentPage.Resources>
+            <x:Array x:Key="stringArray" Type="{x:Type x:String}">
+                <x:String>FirstItem</x:String>
+                <x:String>SecondItem</x:String>
+                <x:String>ThirdItem</x:String>
+            </x:Array>
+        </ContentPage.Resources>
+
+        <StackLayout>
+            <CollectionView ItemsSource="{StaticResource stringArray}"
+                            SelectionMode="Single"
+                            SelectionChanged="CollectionView_SelectionChanged">
+                <CollectionView.ItemTemplate>
+                    <DataTemplate>
+                        <HorizontalStackLayout>
+                            <Image HeightRequest="100"
+                                    WidthRequest="100"
+                                    Source="dotnet_bot.png"/>
+                            <Label AutomationId="{Binding .}"
+                                   Text="{Binding .}"/>
+                        </HorizontalStackLayout>
+                    </DataTemplate>
+                </CollectionView.ItemTemplate>
+            </CollectionView>
+            <Label AutomationId="numberOfNavigations"
+                   x:Name="numberOfNavigationsLabel"
+                   Text="0"/>
+        </StackLayout>
+</ContentPage>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue20273.xaml.cs

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+using System.Threading.Tasks;
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+namespace Maui.Controls.Sample.Issues;
+
+[XamlCompilation(XamlCompilationOptions.Compile)]
+[Issue(IssueTracker.Github, 20273, "Previously selected item cannot be reselected", PlatformAffected.All)]
+
+public partial class Issue20273 : ContentPage
+{
+	int _numberOfNavigations;
+
+	public Issue20273()
+	{
+		InitializeComponent();
+	}
+
+	void CollectionView_SelectionChanged(System.Object sender, Microsoft.Maui.Controls.SelectionChangedEventArgs e)
+	{
+		numberOfNavigationsLabel.Text = (++_numberOfNavigations).ToString();
+	}
+}

src/Controls/tests/UITests/Tests/Issues/Issue20273.cs

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+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.AppiumTests.Issues;
+
+public class Issue20273 : _IssuesUITest
+{
+	public override string Issue => "Previously selected item cannot be reselected";
+
+	public Issue20273(TestDevice device)
+		: base(device)
+	{ }
+
+    [Test]
+	public void PreviouslySelectedItemShouldBeReselected()
+	{
+		var firstItem = App.WaitForElement("FirstItem");
+		firstItem.Click();
+		App.WaitForElement("FirstItem");
+		firstItem.Click();
+		var numberOfNavigations = App.WaitForElement("numberOfNavigations").GetText();
+
+		Assert.AreEqual(int.Parse(numberOfNavigations!), 2);
+	}
+}