Upgrade to Kotlin 1.6.20.

Closes #1691

Author: mp911de

parent/pom.xml

@@ -115,7 +115,7 @@
 		<!-- Deprecated: Use junit-vintage-engine and JUnit 4 is included as transitive dependency -->
 		<junit>4.13.2</junit>
 		<junit5>5.8.2</junit5>
-		<kotlin>1.6.20-RC</kotlin>
+		<kotlin>1.6.20</kotlin>
 		<kotlin-coroutines>1.6.0</kotlin-coroutines>
 		<logback>1.2.5</logback>
 		<lombok>1.18.20</lombok>