Update kotlin monorepo to v2.0.21

Author: renovate[bot]

core/pom.xml

@@ -76,7 +76,7 @@
     <hsqldb.version>2.7.3</hsqldb.version>
     <checkstyle.config>${project.basedir}/checkstyle-override.xml</checkstyle.config>
     <formatter.config>eclipse-formatter-config-4space.xml</formatter.config>
-    <kotlin.version>2.0.20</kotlin.version>
+    <kotlin.version>2.0.21</kotlin.version>
     <junit.jupiter.version>5.11.2</junit.jupiter.version>
     <argLine>-Xmx1024m -Duser.timezone=UTC</argLine>