Update tooling

[FlynnD273]

Update to the latest Jekyll/Ruby version, and the latest SCSS syntax

[Sorixelle]

You'll probably want to rebase this branch, since I've duplicated some of the work here recently (sorry - missed this PR until now 😅).

The main thing here I didn't work on is converting Sass @imports to @use, since that one needs some thinking about how to handle cleanly. Feel free to take some stabs at that issue in this PR, if you'd like!

[Sorixelle]

There's still quite a few conflicts - can you resolve them?

[FlynnD273]

???
Okay seems that I've messed up the merge. Diffs are messed up

[FlynnD273]

Actually maybe I'm just confused lol. It looks like #5305664 is just adding a bunch of files from upstream/main?

[FlynnD273]

Okay. I think everything's working now finally maybe 😭
I still need to do a second pass, reverting the header comment formatting and alphabetising the @use directives but it at least runs now.

[FlynnD273]

Sorry for the huge PR 😢

[Sorixelle]

It looks like a bunch of CSS was duplicated into source/_sass/_site. Can you clean that up?

[FlynnD273]

It looks like a bunch of CSS was duplicated into source/_sass/_site. Can you clean that up?

Yup. I'm not actually sure how those files came to be, I assumed they were born when I merged upstream. But looking at upstream, it seems not so I'm confused 😅