Add CI settings

.github/workflows/ci.yaml

@@ -0,0 +1,40 @@
+name: CI
+on:
+  pull_request:
+  push:
+jobs:
+  test:
+    strategy:
+      fail-fast: false
+      matrix:
+        name: [ "format", "test" ]
+        scala: [ 3.3.0, 3.3.1 ]
+        java: [ 20, 21 ]
+        include:
+          - scala: 3.3.0
+            java: 20
+          - name: "format"
+            scala: 3.3.1
+            java: 21
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-java@v3
+        with:
+          distribution: temurin
+          java-version: ${{ matrix.java }}
+          cache: sbt
+      - shell: bash
+        run: |
+          case ${{ matrix.name }} in
+            "format")
+              sbt -v scalafmtSbt scalafmtAll
+              git diff --exit-code
+              ;;
+            "test")
+              sbt -v test
+              ;;
+            *)
+              echo "unknown job"
+              exit 1
+          esac