Upgrade sbt to allow Scala Steward to run

[rtyley]

We need at least sbt 1.9.0 to run Scala Steward, see:

• Running Scala Steward on a repo at the Guardian maintaining-scala-projects#7

Otherwise the Scala Steward run fails:

2024-10-23 10:41:09,359 ERROR Steward guardian/tagmanager failed
  org.scalasteward.core.io.process$ProcessFailedException: '"SBT_OPTS=-Xmx2048m -Xss8m -XX:MaxMetaspaceSize=512m" sbt -Dsbt.color=false -Dsbt.log.noformat=true -Dsbt.supershell=false -Dsbt.server.forcestart=true ;+ stewardDependencies;reload plugins;stewardDependencies' exited with code 1.
  [info] [launcher] getting org.scala-sbt sbt 1.7.1  (this may take some time)...
  [info] [launcher] getting Scala 2.12.16 (for sbt)...
  [info] welcome to sbt 1.7.1 (Amazon.com Inc. Java 21.0.5)
  error:
    bad constant pool index: 0 at pos: 48454
       while compiling: <no file>
          during phase: globalPhase=<no phase>, enteringPhase=<some phase>
       library version: version 2.12.16
      compiler version: version 2.12.16
    reconstructed args: -classpath /home/runner/.sbt/boot/scala-2.12.16/lib/scala-library.jar -Yrangepos
  
    last tree to typer: EmptyTree
         tree position: <unknown>
              tree tpe: <notype>
                symbol: null
             call site: <none> in <none>

[rtyley]

See:

• Eviction errors on version conflicts in library dependencies / using VersionScheme.Always maintaining-scala-projects#13

In the future, this line of libraryDependencySchemes config will eventually be able to be removed, probably with:

• Upgrading to Play 3.0 maintaining-scala-projects#4

[prout-bot]

Seen on PROD (merged by @rtyley 5 minutes and 19 seconds ago) Please check your changes!