Update JDK version from 17 to 21 in workflow

Author: jemacineiras

.github/workflows/maven-central-push.yml

@@ -46,10 +46,10 @@ jobs:
         with:
           ref: ${{ github.head_ref }}
 
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v2
         with:
-          java-version: "17"
+          java-version: "21"
           distribution: "adopt"
           server-id: ossrh
           server-username: MAVEN_USERNAME