Fix Python dependency versions and do github action pinning

[marcandrechenier]

Is your feature request related to a problem? Please describe.
The goal here is to avoid future issues like the recent LiteLLM CI hack (see https://docs.litellm.ai/blog/security-update-march-2026).

Describe the solution you'd like
For Python dependencies -> fix the versions. Update only when required, ideally after a cold down period after releases (if possible).
For Github action -> do action pinning with SHA instead of version.

Better be safe than sorry :)

[ic-dev21]

You are welcome to flag specific librairies for our review and do a PR if you wish, thank you for bringing this to our attention.

[marcandrechenier]

All right, I'll do that

[marcandrechenier]

I've been busy on other things but I have not forgotten it. I will eventually jump on it when I get a working dev setup again.