Update kotlin monorepo to v2.1.21

Author: renovate[bot]

gradle/libs.versions.toml

@@ -44,5 +44,5 @@ androidx-lifecycle-viewmodel-compose = { module = "org.jetbrains.androidx.lifecy
 
 # build-logic
 build-gradle-plugin = { module = "com.android.tools.build:gradle", version = "8.10.0" }
-kotlin-gradle-plugin = { module = "org.jetbrains.kotlin:kotlin-gradle-plugin", version = "2.1.20" }
-compose-compiler-plugin = { module = "org.jetbrains.kotlin:compose-compiler-gradle-plugin", version = "2.1.20" }
+kotlin-gradle-plugin = { module = "org.jetbrains.kotlin:kotlin-gradle-plugin", version = "2.1.21" }
+compose-compiler-plugin = { module = "org.jetbrains.kotlin:compose-compiler-gradle-plugin", version = "2.1.21" }