mathlib docs are broken again

Stream: general

[Jz Pan]

Seems that it haven't build for 4 days: https://github.com/leanprover-community/mathlib4_docs/actions

[Henrik Böving]

This is because the hoskinson runners are not picking up the jobs, who is responsible for those again?

[Sébastien Gouëzel]

I should have activated two runners to build docs, unless I've messed up.