SecurityToken is not found by .NET Framework project after upgrade of System.ServiceModel.Primitives from 4.10.3 to 8.1.1 in netstandard2.0 project

**Describe the bug**
Version 8.1 of the System.ServiceModel.Primitives brings back netstandard and .NET Framework support to the System.ServiceModel.Primitives package, after it was removed in version 6.0.0. However, after updating the version from 4.10.3 to 8.1.1, when building a .NET Framework project consuming a .NET standard project, exposing the SecurityTopken type in a return parameter, the .NET framework project fails to build with
> Error CS7069: Reference to type 'SecurityToken' claims it is defined in 'System.ServiceModel.Primitives', but it could not be found

**To Reproduce**
Steps to reproduce the behavior:
Build the attached solution: [SecurityTokenNotFound.zip](https://github.com/user-attachments/files/18298108/SecurityTokenNotFound.zip)

**Expected behavior**
The solution should build correctly, as it does when downgrading the System.ServiceModel.Primitives package reference to 4.10.3