Bump org.jetbrains.kotlin.plugin.serialization from 2.1.20 to 2.1.21

Bumps [org.jetbrains.kotlin.plugin.serialization](https://github.com/JetBrains/kotlin) from 2.1.20 to 2.1.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.1.20...v2.1.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin.plugin.serialization
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

build.gradle.kts

@@ -21,7 +21,7 @@ val graphql_kotlin_version = "8.7.0"
 plugins {
     application
     kotlin("jvm") version "2.1.21"
-    id("org.jetbrains.kotlin.plugin.serialization") version "2.1.20"
+    id("org.jetbrains.kotlin.plugin.serialization") version "2.1.21"
     id("com.gradleup.shadow") version "8.3.6"
     id("com.expediagroup.graphql") version "8.7.0"
 }