Update GitHub action for maven build

Author: cchesser

.github/workflows/maven.yml

@@ -19,6 +19,6 @@ jobs:
     - uses: actions/setup-java@v4
       with:
         distribution: 'adopt'
-        java-version: '17'
+        java-version: '21'
     - name: Build with Maven
       run: mvn -B verify --file pom.xml