added Github build workflow

Author: clausnagel

.github/workflows/classindex-build.yml

@@ -0,0 +1,28 @@
+name: xml-objects-build
+
+on: [push, pull_request]
+
+jobs:
+  gradle:
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        java: [21]
+        distribution: [temurin]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+      - name: Setup Java
+        uses: actions/setup-java@v4
+        with:
+          distribution: ${{ matrix.distribution }}
+          java-version: ${{ matrix.java }}
+      - name: Grant execute permission to Gradle
+        run: chmod +x ./gradlew
+      - name: Setup Gradle
+        uses: gradle/actions/setup-gradle@v4
+        with:
+          cache-disabled: true
+      - name: Execute Gradle build
+        run: ./gradlew build