MNT: Github actions, composer requirements, linting

[mfendeksilverstripe]

MISC: Github actions update

• Github actions updated to a more recent setup
• composer requirements refined (minimum requirements)
• fixed linting errors
• removed SASS linting as there are no files to lint
• updated linting rules to match official modules, so we keep things consistent

[mfendeksilverstripe]

@chrispenny Can you please have a look at this one?

[chrispenny]

@mfendeksilverstripe looks good, pending broken checks.

[mfendeksilverstripe]

@chrispenny The failures in the checks are not caused by the changes on this branch - the news checks simply expose pre-existing issues which are:

• composer requirements aren't correctly defined for the low-end (those failing checks are running with oldest possible versions which are allowed via composer)
• looks like there is an issue with the frontend build

I suggest to merge this branch and raise these two as separate issues

[mfendeksilverstripe]

I think this needs a bit more trial and error.

[mfendeksilverstripe]

Managed to fix the low end composer requirements @chrispenny. I think the rest of the issues would be out of scope for this PR.

[chrispenny]

The matrix that ran last week passed, so that might indicate that our existing code works with that particular matrix. If we need to upgrade code in order to upgrade the matrix, then I think that should be done at the same time(?).

[mfendeksilverstripe]

This is back with you @chrispenny for a review. Those 4 last checks require this PR to be merged into master and possibly repo settings update as per https://github.com/orgs/community/discussions/26698