Drop Python 3.7 support

[clenk]

Description

Python 3.7 has reached end of life and is no longer officially supported. We're dropping 3.7 support so need to update mentions of minimum required Python version.

Type of change

• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works