SConstruct: modernize syntax and require Python 3.11 as minimum version #37

Hi,

To be implemented around NVDA 2024.1 release:

I propose modernizing SConstruct file in add-on template to use:

• Formatted string literals (f strings) in places where string interpolations (%s) and str.format are used (unless this introduces security problems)
• Assignment expressions in places where variables are assigned and then used

Also, mark Python 3.11 as the minimum version to run SConstruct.

Thanks,