Update to Elixir 1.18

[jiegillet]

Pretty straightforward, only one kind of warning.
I checked here that we could drop 1.13.

Also closes #1528, except for the elixir school link, but who knows when that will be updated.

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[angelikatyborska]

I think we can merge this one without waiting for the tooling repos, so at least locally you can use 1.18?

[jiegillet]

Sorry, new year food (and maybe the latest Zelda game? 👼) occupied my mind and I didn't check my emails at all last week.
I tweaked the versions while I was at it and I merged it.