Bump minimum supported Python version according to RFC8 policy

According to our Python version support policy, RFC 8 : https://github.com/OSGeo/grass/blob/main/doc/development/rfc/python_language_support.md

We should be bumping the minimum Python version to 3.10, as already done in the main GRASS repository this week.
Python 3.14 was released this week, and 3.9 was supported for a full five years now.