build: updated gh-actions for JDK21

Author: martypitt

.github/workflows/build.yml

@@ -12,10 +12,10 @@ jobs:
 
     steps:
       - uses: actions/checkout@v4
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v4
         with:
-          java-version: '17'
+          java-version: '21'
           distribution: 'temurin'
           cache: maven
       - name: Cache Maven packages