deps: Upgrade Kotlin to version 2.2.21

Author: sschuberth

gradle/libs.versions.toml

@@ -2,7 +2,7 @@
 assertj = "3.27.6"
 git-semver-plugin = "0.16.1"
 jgit = "7.4.0.202509020913-r"
-kotlin = "2.2.0"
+kotlin = "2.2.21"
 plugin-publish = "2.0.0"
 slf4j = "2.0.17"