update to Java 21

Author: AdamBien

cdk/pom.xml

@@ -54,8 +54,8 @@
     </dependencies>
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>17</maven.compiler.source>
-        <maven.compiler.target>17</maven.compiler.target>
-        <java.version>17</java.version>
+        <maven.compiler.source>21</maven.compiler.source>
+        <maven.compiler.target>21</maven.compiler.target>
+        <java.version>21</java.version>
     </properties>
 </project>