Upgrade to Kotlin 1.8.21

Closes gh-35280

Author: wilkinsona

gradle.properties

@@ -4,7 +4,7 @@ org.gradle.caching=true
 org.gradle.parallel=true
 org.gradle.jvmargs=-Xmx2g -Dfile.encoding=UTF-8
 
-kotlinVersion=1.8.20
+kotlinVersion=1.8.21
 nativeBuildToolsVersion=0.9.21
 springFrameworkVersion=6.0.8
 tomcatVersion=10.1.8