Officially support Python 3.9

Environment

• Pythonnet version: latest
• Python version: python 3.9
• Operating System: Windows
• .NET Runtime:

Details

• Describe what you were trying to get done.

My project EddingtonGUI is dependant on Pythonnet. I wanted for quite some time to update it to use Python 3.9 as default, but I noticed that you don't support it yet.

When are you planning on officially supporting Python 3.9? What prevents you from currently supporting it?
I'm asking so I could update my release scheduling accordingly.

Thank you!