github build also needs java 21

Author: jan

.github/workflows/maven.yml

@@ -20,10 +20,10 @@ jobs:
       uses: stCarolas/[email protected]
       with:
         maven-version: 3.9.6
-    - name: Set up JDK 17
+    - name: Set up JDK 21
       uses: actions/setup-java@v4
       with:
-        java-version: '17'
+        java-version: '21'
         distribution: 'adopt'
     - name: Build Sloeber with Maven
       run: mvn --no-transfer-progress verify -Pall,sloeber_release,NOSDK -Dtest=NightlyJenkins -DfailIfNoTests=false