build(deps): Bump org.jetbrains.kotlin:kotlin-gradle-plugin

Bumps [org.jetbrains.kotlin:kotlin-gradle-plugin](https://github.com/JetBrains/kotlin) from 1.8.22 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@v1.8.22...v1.9.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

build.gradle

@@ -2,7 +2,7 @@
 
 buildscript {
     ext {
-        kotlinVersion = '1.8.22'
+        kotlinVersion = '1.9.21'
         commonsVersion = '1.8.2'
     }
     repositories {