Use Java 21 in GitHub workflows

Author: matthewhorridge

.github/workflows/ci.yaml

@@ -8,10 +8,10 @@ jobs:
 
     steps:
       - uses: actions/checkout@v3
-      - name: Set up JDK 17
+      - name: Set up JDK 21
         uses: actions/setup-java@v3
         with:
-          java-version: '17'
+          java-version: '21'
           distribution: 'temurin'
       - name: Build with Maven
         run: mvn --batch-mode --update-snapshots package

.github/workflows/pub-docker-hub.yaml

@@ -17,7 +17,7 @@ jobs:
       - name: Set up Maven Central Repository
         uses: actions/setup-java@v3
         with:
-          java-version: '17'
+          java-version: '21'
           distribution: 'adopt'
           server-id: docker.io
           server-username: DOCKER_USERNAME

.github/workflows/pub.yaml

@@ -11,7 +11,7 @@ jobs:
       - name: Set up Maven Central Repository
         uses: actions/setup-java@v3
         with:
-          java-version: '17'
+          java-version: '21'
           distribution: 'adopt'
           server-id: ossrh
           server-username: OSSRH_USERNAME