GitHub Actions: add CI workflow

.github/workflows/ci.yml

@@ -0,0 +1,33 @@
+name: CI
+on:
+  push:
+    branches:
+      - '*'
+  pull_request:
+    branches:
+      - '*'
+permissions:
+  contents: read
+jobs:
+  ci:
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        os: [ ubuntu-latest, windows-latest, macos-latest ]
+        java: [ 11, 17 ]
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Set up JDK ${{ matrix.java }}
+        uses: actions/setup-java@v1
+        with:
+          java-version: ${{ matrix.java }}
+      - name: Cache local Maven repository
+        uses: actions/cache@v2
+        with:
+          path: ~/.m2/repository
+          key: ${{ runner.os }}-maven-${{ hashFiles('**/pom.xml') }}
+          restore-keys: |
+            ${{ runner.os }}-maven-
+      - name: Build with Maven
+        run: mvn -B verify