backend graphql-core v3 adjustments

[dwsutherland]

partially addresses cylc/cylc-uiserver#333

Sibling to:
cylc/cylc-flow#6478
cylc/cylc-uiserver#672

Can be merged at any point.

This is a small/minor change to handle the JSON parsing of proper enums introduced with graphql-core v3.

Check List

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Tests are included (or explain why tests are not needed).
• Changelog entry not needed
• Docs not needed

[oliver-sanders]

It doesn't quite make sense to me, but it does appear to work.

Suggest keeping this PR open until the upstream PRs have been merged so it can adapt if necessary.

[dwsutherland]

It doesn't quite make sense to me, but it does appear to work.

Suggest keeping this PR open until the upstream PRs have been merged so it can adapt if necessary.

I think it's something like parsing "Live" in contrast to passing "\"Live\"" as JSON?
As the enum argument value isn't quoted it's just mode: Live not mode: "Live" .. not entirely sure
But the new form of enums definitely tripped it up..

[MetRonnie]

We are getting close on the sibling PRs, no reason not to merge this as it is backwards compatible