Revert "Bump Kotlin from 2.3.0 to 2.3.20"

This reverts commit ceea4d6.

Author: leotm

packages/gradle-plugin/gradle/libs.versions.toml

@@ -4,7 +4,7 @@ gson = "2.8.9"
 guava = "31.0.1-jre"
 javapoet = "1.13.0"
 junit = "4.13.2"
-kotlin = "2.3.20"
+kotlin = "2.3.0"
 assertj = "3.25.1"
 ktfmt = "0.22.0"