Update kotlin monorepo to v2.3.20

Author: renovate[bot]

gradle/libs.versions.toml

@@ -1,7 +1,7 @@
 [versions]
 
 # --- Kotlin & Core ---
-kotlin = "2.2.21"            # https://github.com/JetBrains/kotlin
+kotlin = "2.3.20"            # https://github.com/JetBrains/kotlin
 coroutines = "1.10.2"        # https://github.com/Kotlin/kotlinx.coroutines
 serialization = "1.11.0"      # https://github.com/Kotlin/kotlinx.serialization
 kapt = "2.1.0"               # https://kotlinlang.org/docs/kapt.html