Update kotlin monorepo to v2.3.21

Author: renovate[bot]

gradle/libs.versions.toml

@@ -1,7 +1,7 @@
 [versions]
-kotlin = "2.2.21" # Used for the code of the rules
+kotlin = "2.3.21" # Used for the code of the rules
 ktlint = "1.8.0"
-kotlin-ktlint = "2.2.21" # Update only when ktlint version updates
+kotlin-ktlint = "2.3.21" # Update only when ktlint version updates
 detekt = "2.0.0-alpha.3"
 kotlin-detekt = "2.3.21" # Update only when detekt version updates
 junit = "5.14.4"