Update Robot diff GH Action on PRs

[anitacaron]

Remove alternative action to run docker on macos runner. GH increased memory on the ubuntu-latest label, so we can update the diff action to use ubuntu-latest.

This also align more closely to the same action available in CL.

• Add branch status job before generating diff
• Create different jobs

It's also updated to generate the classified ontology on the base, which is now the case.

Technically fixes #3183

[matentzn]

I cannot see anything glaringly wrong, but my review was a C- in terms of rigour. I think the risk is low to merge and then try.