add GitHub Actions workflow

.github/workflows/ci.yml

@@ -0,0 +1,36 @@
+name: CI
+
+on:
+  push:
+    branches: ['main']
+  pull_request:
+    branches: ['**']
+
+jobs:
+
+  build:
+    strategy:
+      matrix:
+        java: [ '8' ]
+        jdk: [ 'temurin' ]
+        os: [ 'ubuntu-latest' ]
+    runs-on: ${{ matrix.os }}
+    name: Java ${{ matrix.java }} ${{ matrix.jdk }}
+    steps:
+      - name: Check out code
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: '0'
+
+      - name: Gradle wrapper validation
+        uses: gradle/wrapper-validation-action@v2
+
+      - name: Set up Java
+        uses: actions/setup-java@v4
+        with:
+          java-version: ${{ matrix.java }}
+          distribution: ${{ matrix.jdk }}
+          cache: 'gradle'
+
+      - name: Gradle build
+        run: ./gradlew clean build