Animation.Repeat property set to Forever plays only once #840

Describe the bug

I tried to use a repeating animation but it seems to only play once, ignoring the Forever option being set.

Steps to reproduce

This is all you need as code to reproduce the issue:

<StackPanel Orientation="Horizontal" VerticalAlignment="Center" HorizontalAlignment="Center" Spacing="16">

    <StackPanel.Resources>
        <a:AnimationSet x:Key="PulsateAnimation">
            <a:ScalarAnimation Target="Opacity" Duration="0:0:2" Repeat="Forever">
                <a:ScalarKeyFrame Key="0" Value="1"/>
                <a:ScalarKeyFrame Key="0.5" Value="0"/>
                <a:ScalarKeyFrame Key="1" Value="1"/>
            </a:ScalarAnimation>
        </a:AnimationSet>
    </StackPanel.Resources>

    <Button Content="Click me to animate">
        <i:Interaction.Behaviors>
            <i:EventTriggerBehavior EventName="Click">
                <b:StartAnimationAction Animation="{StaticResource PulsateAnimation}"  TargetObject="{x:Bind StateIcon}"/>
            </i:EventTriggerBehavior>
        </i:Interaction.Behaviors>
    </Button>

    <FontIcon x:Name="StateIcon"
        VerticalAlignment="Center"
        Glyph="&#x25CF;"
        FontFamily="{ThemeResource ContentControlThemeFontFamily}"
        FontSize="14"
        Foreground="{ThemeResource SystemFillColorCautionBrush}">
    </FontIcon>
</StackPanel>

Expected behavior

I would expect the Forever value for the Repeat property to loop the animation until is stopped.

Screenshots

No response

Code Platform

• UWP
• WinAppSDK / WinUI 3
• Web Assembly (WASM)
• Android
• iOS
• MacOS
• Linux / GTK

Windows Build Number

• Windows 10 1809 (Build 17763)
• Windows 10 1903 (Build 18362)
• Windows 10 1909 (Build 18363)
• Windows 10 2004 (Build 19041)
• Windows 10 20H2 (Build 19042)
• Windows 10 21H1 (Build 19043)
• Windows 10 21H2 (Build 19044)
• Windows 10 22H2 (Build 19045)
• Windows 11 21H2 (Build 22000)
• Other (specify)

Other Windows Build number

26200.8117

App minimum and target SDK version

• Windows 10, version 1809 (Build 17763)
• Windows 10, version 1903 (Build 18362)
• Windows 10, version 1909 (Build 18363)
• Windows 10, version 2004 (Build 19041)
• Windows 10, version 2104 (Build 20348)
• Windows 11, version 22H2 (Build 22000)
• Other (specify)

Other SDK version

No response

Visual Studio Version

No response

Visual Studio Build Number

18.4.3

Device form factor

Desktop

Additional context

I tested with CommunityToolkit.WinUI.Behaviors version 8.3.260402-preview2 and stable version 8.2.251219.

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