XmlnsDefinition not working in HeadlessPlattform

[IXimonI]

Describe the bug

I'm getting this issue when running UnitTests using Avalonia.Headless(.Xunit).

XamlX.XamlParseException: 'Unable to resolve type Xyz from namespace Abc

The issue is not appearing in normal app setups and can be solved using the workaround described in #7200
( GC.KeepAlive(typeof(TypeInReferencedAssembly)) in App.OnFrameworkInitializationCompleted() )

I guess this is also a similar issue to the solved #7200 thus only appearing in this specific setup.

To Reproduce

1. Prepare an AssemblyInfo with XmlnsDefinition Attribute for the library you want to test e.g.

using Avalonia.Metadata;
[assembly: XmlnsDefinition("https://my.controls.url", "Abc.Namespace")]

2. Try test it in an Avalonia.Headless testing project for example parsing a Xaml:

Expected behavior

All types beeing resolved. Can be currently reached by modifing the TestApp type like this (line 20):

Thank you for your help

Avalonia version

11.0.10

OS

Windows

Additional context

No response