Update kotlin to 2.1.21

Author: mlykotom

get-started/gradle/libs.versions.toml

@@ -20,7 +20,7 @@ agp = "8.10.1"
 androidx-activityCompose = "1.10.1"
 androidx-room = "2.6.1"
 androidx-lifecycle = "2.8.7"
-kotlin = "2.1.10"
+kotlin = "2.1.21"
 kotlinx-coroutines = "1.10.2"
 spotless = "7.0.3"
 composeBom = "2025.06.00"