Cannot process input of abstract type 'microsoft.graph.extension'

Describe the bug

Hello,

I am trying to load an Extension for a Contact, Change a Value then save it, but i am getting the Error in the title.
I found this (https://github.com/microsoftgraph/msgraph-sdk-dotnet/issues/1723) issue before, but there, a contact is loaded and then the Extension is changed.
In my case, i am loading the Extension and nothing else.

Expected behavior

not getting an error i guess?

How to reproduce

var extension = (await _graphClient.Me.ContactFolders["MyContactFolderId"].Contacts["MyContactId"].Extensions["MyExtension"].GetAsync()) as OpenTypeExtension;
extension.AdditionalData["MyProperty"] = "MyNewValue";
await _graphClient.Me.ContactFolders["MyContactFolderId"].Contacts["MyContactId"].Extensions["MyExtension"].PatchAsync(extension);

SDK Version

5.54.0

Latest version known to work for scenario above?

Unknown

Known Workarounds

None

Debug output

</details>


### Configuration

- OS: Windows 10
- Architecture: x64 (AMD Ryzen 7 1700)

### Other information

_No response_

Start with the reproduction in the issue using Microsoft Graph SDK .NET 5.54.0, focusing on loading an extension and then calling PatchAsync after changing AdditionalData. Trace the extension response and request handling to find why the abstract microsoft.graph.extension type is used. Done means the shown OpenTypeExtension flow patches the changed contact extension without the abstract-type error.