5.56.0 breaks ExternalConnectors.DisplayTemplate.Layout with UntypedNode

Describe the bug

Code that worked and compiled fine before to set a display template on an ExternalConnection now gives the error:

C:\Source\Repos\msgraph-sample-github-connector-dotnet\src\Services\SearchConnectorService.cs(154,29): error CS0117: 'UntypedNode' does not contain a definition for 'AdditionalData' [C:\Source\Re
pos\msgraph-sample-github-connector-dotnet\src\GitHubConnector.csproj]

Expected behavior

Code should continue to compile and work.

How to reproduce

Sample that repros error: https://github.com/microsoftgraph/msgraph-sample-github-connector-dotnet

Relevant line: https://github.com/microsoftgraph/msgraph-sample-github-connector-dotnet/blob/20d80700de852245edb16c44a73cb2ed53d436b8/src/Services/SearchConnectorService.cs#L154

SDK Version

5.56.0

Latest version known to work for scenario above?

5.55.0

Known Workarounds

No response

Debug output

</details>


### Configuration

_No response_

### Other information

_No response_

Start with the linked sample at src/Services/SearchConnectorService.cs around line 154 and build it against Microsoft Graph SDK 5.56.0 to reproduce the UntypedNode.AdditionalData error. Compare the relevant behavior with SDK 5.55.0 and inspect the ExternalConnectors.DisplayTemplate.Layout types. Done means the sample compiles and the display template still works on an ExternalConnection.