Use pak instead of remotes

vise has [recently been updated](https://github.com/carpentries/vise/pull/12) to use pak when updating the renv lockfile. This is in order to better pick up system dependencies that might have arisen as part of a commit, but are not yet part of the lockfile in the repo. This will also address #41 here.

However, some parts of the actions here still use remotes, which could do with being moved over to pak for consistency.