Python 3.9 EOL

[JCGoran]

Python 3.9 will reach end-of-life (EOL) in October 2025, so we should bump the minimum supported Python version to 3.10.
The following repos need to be updated:

• this one
• https://github.com/neuronsimulator/nrn-build-ci
• https://github.com/neuronsimulator/nrn-modeldb-ci