Install quarto (instead of pandoc) on win/mac ?

[jeroen]

We have quarto on the Linux image to build vignettes, but some packages also want it on Win/Mac.

https://github.com/r-universe/ropensci/actions/runs/12159892618

Quarto is quite big so it adds some build time to install it on every run. However it also includes a copy of pandoc so perhaps we do not have to install this separately anymore, if we can put it all on the path somehow.