Use curl instead of wget in pre-render

[NeuroShepherd]

pre-render: curl -O -L --insecure https://raw.githubusercontent.com/lmu-osc/branding-resources/refs/heads/main/lmu-osc-custom.scss

[NeuroShepherd]

More generally, would like to get rid of this approach and just have an SCSS file in each repo.

This hacky approach is only used because Quarto needs the SCSS variables to be defined when rendering, and can't pull from a remote source the way one could specify e.g. a remote CSS file.