chore(deps): update plugin org.jetbrains.kotlin.plugin.spring to v2.0.21 (#142)

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

Author: renovate[bot]

build.gradle.kts

@@ -5,7 +5,7 @@ import org.jetbrains.kotlin.gradle.tasks.KotlinCompile
 plugins {
     id("org.springframework.boot") version "3.3.4"
     kotlin("jvm") version "2.0.20"
-    kotlin("plugin.spring") version "2.0.20"
+    kotlin("plugin.spring") version "2.0.21"
 
     // graphql plugins
     id("com.expediagroup.graphql") version "8.1.0"