update java to 21

Author: hohwille

.github/workflows/build-pr.yml

@@ -11,7 +11,7 @@ jobs:
       - name: Set up JDK
         uses: actions/setup-java@v3
         with:
-          java-version: '17'
+          java-version: '21'
           distribution: 'temurin'
       - name: Build project with Maven
         run: mvn -B -ntp install

.github/workflows/build.yml

@@ -13,7 +13,7 @@ jobs:
       - name: Set up JDK
         uses: actions/setup-java@v3
         with:
-          java-version: '17'
+          java-version: '21'
           distribution: 'temurin'
       - name: Build project with Maven
         run: mvn -B -ntp install