Revert "Build Spring Batch Notion with Java 25"

This reverts commit 4721385.

Author: scordio

.github/workflows/spring-batch-notion.yml

@@ -20,7 +20,7 @@ jobs:
         uses: actions/setup-java@v4
         with:
           distribution: 'temurin'
-          java-version: '25'
+          java-version: '21'
           cache: 'maven'
       - name: Build with Maven
         run: ./mvnw $MAVEN_ARGS verify javadoc:javadoc