Github pages artifacts

[IAlibay]

Github pages is leaving behind quite a lot of artifacts (31 since April)

For full list see:

curl \
  -H "Accept: application/vnd.github.v3+json" \
  https://api.github.com/repos/MDAnalysis/mdanalysis/actions/artifacts

They have a retention limit of 90 days, but it might make sense to lower that retention limit to a week just to keep the artifact list clean?

@lilyminium is this something that is feasible?