ci: Use guardian/setup-scala GitHub Action

This action will provide Java and SBT to the runner.
This is a mitigation against the incoming changes from GitHub where the `ubuntu-latest` runner will stop providing `sbt` by default.

See:
- https://github.com/guardian/setup-scala
- https://github.blog/changelog/2024-11-05-notice-of-breaking-changes-for-github-actions/
- https://github.com/actions/runner-images#10636

.github/workflows/ci.yml

@@ -26,12 +26,8 @@ jobs:
           cache: 'npm'
           cache-dependency-path: 'cdk/package-lock.json'
 
-      # Java is needed for the Scala Play app
-      - name: Set up Java
-        uses: actions/setup-java@v4
-        with:
-          java-version: '11' # TODO read this from the `.java-version` file in the repository
-          distribution: 'corretto'
+      - uses: guardian/setup-scala@v1
+
       - run: ./scripts/ci
 
       - uses: guardian/actions-riff-raff@v4

.github/workflows/sbt-dependency-graph.yaml

@@ -11,15 +11,7 @@ jobs:
       - name: Checkout branch
         id: checkout
         uses: actions/checkout@eef61447b9ff4aafe5dcd4e0bbf5d482be7e7871 # v4.2.1
-      - name: Install Java
-        id: java
-        uses: actions/setup-java@b36c23c0d998641eff861008f374ee103c25ac73 # v4.2.0
-        with:
-          distribution: corretto
-          java-version: 17
-      - name: Install sbt
-        id: sbt
-        uses: sbt/setup-sbt@50a38cca700907fb9df65ecabcefb85ebaa424a7 # v1.1.4
+      - uses: guardian/setup-scala@v1
       - name: Submit dependencies
         id: submit
         uses: scalacenter/sbt-dependency-submission@64084844d2b0a9b6c3765f33acde2fbe3f5ae7d3 # v3.1.0

.tool-versions

@@ -0,0 +1 @@
+java corretto-11.0.25.9.1