Julia 1.10 is now LTS instead of 1.6, consequences for us

[fingolfin]

Julia 1.10 is now the Julia LTS release.

Should we draw consequences from this? Some we might want to consider:

1. we might raise the minimal required version for OSCAR from 1.6 to something higher, possibly even 1.10
   • pro: some features (e.g. package extensions) don't work in 1.6
   • con: excludes users (does the gain justify it?)
   • more pros/cons?
2. we may wish to stop CI testing with 1.6 (even if we don't explicitly drop 1.6 support), as work needed for supporting it will increase over time
   • e.g. we just needed https://github.com/oscar-system/Oscar.jl/pull/4189 and a similar change now is required fro all our other packages that run OscarCI on Julia 1.6 as part of their CI tests.
   • to stick with my example from above: package extensions require Julia 1.9 so we could decide to use that as minimal version

To be clear: I am not strongly advocating for this, but the question came up in Slack and I think it would be good to make our plans on this explicit.

(Personally I wonder if it might be a bit soon for requiring 1.10, given that it was released Dec 26, 2023 and so is not even a year old. OTOH if people use juliaup as they IMHO should there isn't much of a reason why they couldn't just update to 1.10... )