Test vs Java 21

.github/workflows/test_java_21.yml

@@ -0,0 +1,23 @@
+name: Test Java 21
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build:
+
+    runs-on: ubuntu-latest
+
+    steps:
+    - uses: actions/checkout@v4
+    - name: Set up JDK 21
+      uses: actions/setup-java@v4
+      with:
+        java-version: '21'
+        distribution: 'temurin'
+        cache: 'maven'
+    - name: Build with Maven
+      run: mvn -nsu -B install