restore kotlin version

Author: hauner

gradle/libs.versions.toml

@@ -6,7 +6,7 @@ test-jdk = "17"
 build-plugins = "2026.1"
 
 # using the embedded kotlin version of Gradle to avoid mixed versions
-kotlin = "2.3.0"
+kotlin = "2.2.21"
 checker = "3.53.0"
 checkerp = "0.6.61"
 jacoco = "0.8.11"