Set up SBT in GitHub Actions since it is no longer included in the build image

Author: Abhijit Sarkar

.github/workflows/ci.yml

@@ -14,6 +14,8 @@ jobs:
         with:
           distribution: temurin
           java-version: 17
+      - name: Set up SBT
+        uses: sbt/setup-sbt@v1
       - name: Test
         run: ./.github/run.sh --no-lint
       - name: Lint

.gitignore

@@ -15,6 +15,7 @@ project/local-plugins.sbt
 .ensime_cache/
 .sbt-scripted/
 local.sbt
+out
 
 # Bloop
 .bsp