carpentries/varnish

AI Summary: Update the CSS for the Carpentries Workbench's `varnish` package to change the color of list item text from black (#000000) to dark grey (#383838) to match the main body text color and improve readability. This involves locating the relevant CSS rule within the `source/` directory, modifying the color property, and rebuilding the minified CSS using the provided `squash-sass.sh` script.