GH-2317 - Update Kotlin to 2.1.20.

Author: odrotbohm

Diff for: pom.xml

@@ -85,7 +85,7 @@
 		<slf4j.version>2.0.17</slf4j.version>
 		<spring.version>7.0.0-M4</spring.version>
 		<spring-plugin.version>4.0.0-SNAPSHOT</spring-plugin.version>
-		<kotlin.version>2.1.0</kotlin.version>
+		<kotlin.version>2.1.21-RC</kotlin.version>
 		<kotlinx-coroutines.version>1.10.2</kotlinx-coroutines.version>
 		<mockk.version>1.14.0</mockk.version>
 	</properties>