Update GHA JDK to the latest LTS version (21)

Author: SimonMarquis

.github/workflows/Build.yaml

@@ -29,11 +29,11 @@ jobs:
       - name: Copy CI gradle.properties
         run: mkdir -p ~/.gradle ; cp .github/ci-gradle.properties ~/.gradle/gradle.properties
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v4
         with:
           distribution: 'zulu'
-          java-version: 17
+          java-version: 21
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v4
@@ -180,11 +180,11 @@ jobs:
       - name: Copy CI gradle.properties
         run: mkdir -p ~/.gradle ; cp .github/ci-gradle.properties ~/.gradle/gradle.properties
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v4
         with:
           distribution: 'zulu'
-          java-version: 17
+          java-version: 21
 
       - name: Setup Gradle
         uses: gradle/actions/setup-gradle@v4