Bump org.jetbrains.kotlin.jvm in /plugins/gradle/example-client-kotlin (#1421)

Bumps [org.jetbrains.kotlin.jvm](https://github.com/JetBrains/kotlin) from 1.9.20 to 1.9.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.9.20...v1.9.21)

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

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

plugins/gradle/example-client-kotlin/build.gradle

@@ -3,7 +3,7 @@ import io.github.kobylynskyi.graphql.codegen.gradle.GraphQLCodegenGradleTask
 
 plugins {
     id "java"
-    id "org.jetbrains.kotlin.jvm" version "1.9.20"
+    id "org.jetbrains.kotlin.jvm" version "1.9.21"
     id "io.github.kobylynskyi.graphql.codegen" version "5.9.1-SNAPSHOT"
 }