Upgrade to Kotlin 1.5.21.

See #1488

Author: mp911de

parent/pom.xml

@@ -112,7 +112,7 @@
 		<!-- Deprecated: Use junit-vintage-engine and JUnit 4 is included as transitive dependency -->
 		<junit>4.13.2</junit>
 		<junit5>5.7.1</junit5>
-		<kotlin>1.5.20</kotlin>
+		<kotlin>1.5.21</kotlin>
 		<kotlin-coroutines>1.5.1</kotlin-coroutines>
 		<logback>1.2.3</logback>
 		<lombok>1.18.20</lombok>