Update dependency org.jetbrains.kotlin.multiplatform to v2.0.21 (#774)

Author: juul-mobile-bot

gradle/libs.versions.toml

@@ -4,7 +4,7 @@ android-min = "21"
 atomicfu = "0.25.0"
 coroutines = "1.9.0"
 jvm-toolchain = "11"
-kotlin = "2.0.20"
+kotlin = "2.0.21"
 tuulbox = "8.0.0"
 
 [libraries]