MNT Fix CI

[emteknetnz]

Issue silverstripe/gha-ci#37

I think it's still worth keeping the ci.yml file, if only so we don't need to wonder why in the future it has not run for years

[GuySartorelli]

Might be worth creating a new issue (either here or in gha-ci) to find a way around this, and just have a comment pointing to that issue.
Also probably set this to not run on PRs - it's a bit weird to see a green test on the PR when nothing is actually being tested - it makes it seem like the PR may be safer than it really is and means we're less likely to check, for example, if the dist files are actually in the PR.

[emteknetnz]

It is weird, though I'd rather have a null CI run on pull-requests that no CI at all. That way it's consistent with every other module that has a CI run and we don't need to every investigate why the CI never run.

Have created issue #150

[GuySartorelli]

Yeah I don't like it but it's not the end of the world. I'll merge.