build(deps): bump org.jetbrains.kotlin.jvm in /code_samples/kotlin_demo (#1154)

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](https://github.com/JetBrains/kotlin/compare/v1.9.20...v1.9.21)

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

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

kotlin_demo/build.gradle.kts

@@ -3,7 +3,7 @@
 plugins {
   id("java")
   id("org.jetbrains.intellij") version "1.16.0"
-  id("org.jetbrains.kotlin.jvm") version "1.9.20"
+  id("org.jetbrains.kotlin.jvm") version "1.9.21"
 }
 
 group = "org.intellij.sdk"