Update release.yml to Java 21

Author: rensink

.github/workflows/release.yml

@@ -31,10 +31,10 @@ jobs:
       with:
         repository: 'nl-utwente-groove/samples'
         path: 'samples'
-    - 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: Install local packages