Scala Steward can not run on this repo until it allows building under Java 21

[rtyley]

See guardian/scala-steward-public-repos#67 ... we're now running our Scala Steward workflow with Java 21 LTS, which means that all projects that want to have Scala Steward updates (like this one) need to be able to build under Java 21 (even if the projects are still running in production on Java 8).

An example of Scala Steward failing when trying to handle this repo is here:

https://github.com/guardian/scala-steward-public-repos/actions/runs/8814650168/job/24194965264#step:6:1970

[info] [launcher] getting org.scala-sbt sbt 1.5.8 (this may take some time)...
[info] [launcher] getting Scala 2.12.14 (for sbt)...
java.lang.ClassCastException: class java.lang.UnsupportedOperationException cannot be cast to class xsbti.FullReload (java.lang.UnsupportedOperationException is in module java.base of loader 'bootstrap'; xsbti.FullReload is in unnamed module of loader 'app')

Unfortunately the Scala Steward run failing affects everyone, see guardian/scala-steward-public-repos#60 - so I've removed this repo from Scala Steward until this issue is fixed.

How to fix this issue?

For the buid to run under Java 21, a few things are easy, but some are a bit more involved:

• Easy: Update Scala (2.12.18+) & sbt (1.9.0+)
• Hard: Cope with updates to JAXB that come with Java 9 and above - the JAXB library is no longer a core part of Java, and the sbt-cxf plugin has not been updated in a long time and isn't compiled for that change. I think the best bet here may be to move to using scalaxb, which is maintained and can probably provide the WSDL/XML parsing that is required - it could be tricky though, let me know if you'd like to pair on it.

cc @LAKSHMIRPILLAI @tomrf1

[tomrf1]

Thanks @rtyley , we did briefly look at upgrading java but parked it, so your advice regarding jaxb is really helpful!

[rtyley]

Ah, I've taken a look at this, and think I can help- alright if I raise a PR?

[tomrf1]

of course! We have a health ticket for it but you're more than welcome to contribute :)