Bump scikit-learn version to 1.6

[ArturoAmorQ]

We currently use scikit-learn v1.3, but #772 requires v1.4. Updating scikit-learn to its latest version (v1.6) will allow us to give a better maintenance to the mooc.

On FUN, updating the Jupyter image of the students seems to suffice.

[lesteve]

Not sure about the implications on the FUN MOOC if any, but I'll let you deal with this 😉

[lesteve]

Thinking about it more, I guess for now none of our notebooks actually need scikit-learn 1.6 but oh well ...