Update 'anaconda' module in 'docs/user-guide/python.md'

[mikej888]

docs/user-guide/python.md states:

As described above, load the Anaconda module on Cirrus using module load anaconda3/2023.9.

This is the only reference to anaconda3/2023.9 on the page. The command fails:

$ module load anaconda3/2023.9
ERROR: Unable to locate a modulefile for 'anaconda3/2023.9'

The following works:

$ module load anaconda3
$ python --version
Python 3.11.5