CI install bibtools

Stream: mathlib4

[Damiano Testa]

I am pretty sure that this step did not take over 15 minutes to complete!

https://github.com/leanprover-community/mathlib4/actions/runs/10791576513/job/29929280087?pr=16659

[Markus Himmel]

Some CI runners are having trouble connecting to the Azure Ubuntu mirror at the moment. This affects other repositories as well (for example the Lean 4 core repo). It will probably be fixed soon.

[Damiano Testa]

Ok, thanks for the explanation!