Fix Python.NET GIL shutdown finalizer crash

[jassim1977]

Description

Removes an undisposed Py.GIL() acquisition immediately before PythonEngine.Shutdown().

With Python.Runtime 2.0.66 and Python 3.11.16 on Windows, the retained GIL state reaches finalization after engine shutdown and raises:

System.InvalidOperationException: GIL must always be released, and it must be released from the same thread that acquired it.

Reproduction before fix

• Python algorithm initializes and completes its backtest.
• Shutdown reaches PythonInitializer.Shutdown().
• Process terminates from Py.GILState.Finalize().
• Exit code: -532462766.

Validation after fix

• Full LEAN Release build: 0 errors.
• Five Python algorithm scenarios completed with exit code 0.
• Five of five runs reached PythonInitializer.Shutdown(): ended.
• Repeated allow scenario completed successfully across five runs.
• No GIL must always be released failure occurred.
• Allow scenario submitted and filled exactly one order.
• Four rejection scenarios submitted no orders.

This change is intentionally limited to one line in PythonInitializer.Shutdown().