fix: Install sbt in GitHub workflow

Adds a step to explicitly install sbt using apt-get in the GitHub Actions
workflow (.github/workflows/scala.yml). This is done for both the 'test'
and 'lint' jobs after Java has been set up.

This addresses the 'sbt: command not found' error encountered in previous
workflow runs.

Author: google-labs-jules[bot]

.github/workflows/scala.yml

@@ -11,6 +11,13 @@ jobs:
           java-version: '11'
           distribution: 'temurin'
           cache: 'sbt'
+      - name: Install sbt
+        run: |
+          echo "deb https://repo.scala-sbt.org/scalasbt/debian all main" | sudo tee /etc/apt/sources.list.d/sbt.list
+          echo "deb https://repo.scala-sbt.org/scalasbt/debian /" | sudo tee /etc/apt/sources.list.d/sbt_old.list
+          curl -sL "https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x2EE0EA64E40A89B84B2DF73499E82A75642AC823" | sudo apt-key add -
+          sudo apt-get update
+          sudo apt-get install -y sbt
       - name: Run tests
         run: sbt coverage test
       - name: Coverage Report
@@ -29,5 +36,12 @@ jobs:
           java-version: '11'
           distribution: 'temurin'
           cache: 'sbt'
+      - name: Install sbt
+        run: |
+          echo "deb https://repo.scala-sbt.org/scalasbt/debian all main" | sudo tee /etc/apt/sources.list.d/sbt.list
+          echo "deb https://repo.scala-sbt.org/scalasbt/debian /" | sudo tee /etc/apt/sources.list.d/sbt_old.list
+          curl -sL "https://keyserver.ubuntu.com/pks/lookup?op=get&search=0x2EE0EA64E40A89B84B2DF73499E82A75642AC823" | sudo apt-key add -
+          sudo apt-get update
+          sudo apt-get install -y sbt
       - name: Formatting
         run: sbt scalafmtSbtCheck scalafmtCheck test:scalafmtCheck