CumulusCI / Selenium 3 is incompatible with python 3.9

[sam-nolan-tearfund]

Describe the bug

Currently, Running Choose File from Selenium Library in python 3.9 and above will fail with the following error when connected to selenium hub:

LOG FAILAttributeError: module 'base64' has no attribute 'encodestring'

This is because selenium 3 does not support python 3.9, however, this package depends on selenium 3.

Reproduction steps

1. Install python 3.9+
2. Install cumulusci
3. Connect to Selenium Hub via Open Browser
4. Run Choose File

Your CumulusCI and Python versions

Cumulusci version 3.90
robotframework version 7.0
robotframework-seleniumlibrary 5.1.3
Python 3.9

Operating System

Windows

Windows environment

WSL

CumulusCI installation method

pip

Error Gist

No response

Additional information

No response