Use Python 3.13 up from 3.11 across the repo

[consideRatio]

We are currently using 3.11 in quite a bit of places:

• GitHub workflow's jobs test environments etc
• Helm chart's docker images
• Maybe more?

We should update to use Python 3.13 instead, or Python 3.12 if its not possible yet to get things to function with Python 3.13.

[consideRatio]

Almost fully resolved now, what remains is blocked on dask-sphinx-theme in dask/dask-sphinx-theme#68