Add CI workflow for testing builds.

.github/workflows/ci.yml

@@ -0,0 +1,25 @@
+name: CI
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  build-and-test:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java: [ 21 ]
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: set up JDK ${{ matrix.java }}
+        uses: actions/setup-java@v4
+        with:
+          java-version: ${{ matrix.java }}
+          distribution: zulu
+          cache: "gradle"
+      - name: Run Build
+        run: ./gradlew shadowJar