Update to using python 3.9

[baolanlequang]

Due to python 3.7 is end of life and python 3.8 will be end of support on October 2024, we need to update python version 3.9 and dependencies that Chemspectra are using.

[harivyasi]

Hi @baolanlequang On a related note, is it possible to remove the list of pip dependencies from environment.yml and include reference to requirements.txt instead? See here for more. This will make packaging easier because there will a single source of truth.