Update plugin org.jetbrains.kotlin.jvm to v2.1.21 (#39)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

build.gradle.kts

@@ -1,7 +1,7 @@
 import org.jetbrains.kotlin.gradle.dsl.JvmTarget
 
 plugins {
-    kotlin("jvm") version "2.1.20"
+    kotlin("jvm") version "2.1.21"
 
     java
     `maven-publish`