Random crash on engine shutdown: 'clr' has no attribute '_add_pending_namespaces'

### Environment

-   Pythonnet version: dee41b8
-   Python version: Any
-   Operating System: Windows x86
-   .NET Runtime: .NET Framework

### Details

  Error Message:
   Python.Runtime.PythonException : partially initialized module 'clr' has no attribute '_add_pending_namespaces' (most likely due to a circular import)

