Update dependency org.jetbrains.kotlin:kotlin-maven-plugin to v1.9.21

Author: renovate[bot]

kotlin/pom.xml

@@ -13,7 +13,7 @@
 	<description>CleanThat for Kotlin code - It enables refactoring automatically Kotlin code</description>
 
 	<properties>
-		<kotlin.version>1.9.20</kotlin.version>
+		<kotlin.version>1.9.21</kotlin.version>
 		<kotlinx.version>1.6.4</kotlinx.version>
 		<!-- https://kotlinlang.org/docs/maven.html#incremental-compilation -->
 		<kotlin.compiler.incremental>true</kotlin.compiler.incremental>