python3.9 dev image #438

Hello.

During the development of Python 3.8, you regularly had images containing dev releases of Python 3.8. This turned out to be incredibly useful for me with the library I am developing, as I was able to automate testing of the library on Python3.8 before it was officially released in my CI pipeline.

Mostly wondering if/when you plan to do the same for Python3.9, if at all.

Thanks :-)