chore(deps): bump kotlin_version from 2.0.20 to 2.0.21 (#663)

Bumps `kotlin_version` from 2.0.20 to 2.0.21.

Updates `org.jetbrains.kotlin:kotlin-reflect` from 2.0.20 to 2.0.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v2.0.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.0.20...v2.0.21)

Updates `org.jetbrains.kotlin.jvm` from 2.0.20 to 2.0.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v2.0.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.0.20...v2.0.21)

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

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

build.gradle

@@ -1,7 +1,7 @@
 buildscript {
     ext.kafka_version = '3.8.0'
     ext.scala_version = '2.13'
-    ext.kotlin_version = '2.0.20'
+    ext.kotlin_version = '2.0.21'
     ext.unboundid_version = '7.0.1'
     ext.caffeine_version = '3.1.8'
     ext.jackson_version = '2.18.0'