chore(deps): update plugin org.jetbrains.kotlin.multiplatform to v2.1.21

Author: renovate[bot]

build.gradle.kts

@@ -3,7 +3,7 @@ import org.jetbrains.kotlin.gradle.targets.js.nodejs.NodeJsRootPlugin.Companion.
 import org.jetbrains.kotlin.gradle.targets.js.yarn.yarn
 
 plugins {
-    kotlin("multiplatform") version "2.1.20"
+    kotlin("multiplatform") version "2.1.21"
     kotlin("plugin.serialization") version "2.1.20"
     id("io.kotest.multiplatform") version "6.0.0.M3"
     distribution