Add build workflow

.github/workflows/build.yml

@@ -0,0 +1,27 @@
+name: Build
+on:
+  push:
+    branches: [ "**" ]
+  pull_request:
+
+jobs:
+  build:
+    # Only run on PRs if the source branch is on someone else's repo
+    if: ${{ github.event_name != 'pull_request' || github.repository != github.event.pull_request.head.repo.full_name }}
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        java: [ 21 ]
+      fail-fast: true
+    steps:
+      - uses: actions/checkout@v4
+      - uses: gradle/wrapper-validation-action@v2
+      - name: JDK ${{ matrix.java }}
+        uses: actions/setup-java@v4
+        with:
+          java-version: ${{ matrix.java }}
+          distribution: 'temurin'
+      - name: Setup Gradle
+        uses: gradle/actions/setup-gradle@v3
+      - name: Build
+        run: ./gradlew build