Update Kotlin to v2.1.21

Author: renovate[bot]

gradle/libs.versions.toml

@@ -5,7 +5,7 @@ bytebuddy = "1.17.5"
 compose = "1.8.1"
 coroutines = "1.10.2"
 javaTarget = "17"
-kotlin = "2.1.20"
+kotlin = "2.1.21"
 ksp = "2.1.20-2.0.1"
 layoutlib = "15.2.2"
 moshi = "1.15.2"