Use Java 21 in CI

.github/workflows/gradle.yml

@@ -3,20 +3,25 @@
 
 name: Java CI with Gradle
 
-on: [ push, pull_request ]
+on: [push, pull_request]
 
 jobs:
   build:
-
+    strategy:
+      matrix:
+        java: [21]
     runs-on: ubuntu-latest
-
     steps:
-    - uses: actions/checkout@v2
-    - name: Set up JDK 1.8
-      uses: actions/setup-java@v1
+    - name: Checkout repository
+      uses: actions/checkout@v4
+    - name: Validate Gradle wrapper
+      uses: gradle/wrapper-validation-action@v2
+    - name: Set up JDK ${{ matrix.java }}
+      uses: actions/setup-java@v4
       with:
-        java-version: 1.8
-    - name: Grant execute permission for gradlew
+        java-version: ${{ matrix.java }}
+        distribution: microsoft
+    - name: Grant execute permission for Gradle wrapper
       run: chmod +x gradlew
     - name: Test with Gradle
-      run: ./gradlew test && ./gradlew build
+      run: ./gradlew test