Bump kotlinVersion from 2.1.20 to 2.1.21 (#3892)

Bumps `kotlinVersion` from 2.1.20 to 2.1.21.

Updates `org.jetbrains.kotlin:kotlin-gradle-plugin` 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](https://github.com/JetBrains/kotlin/compare/v2.1.20...v2.1.21)

Updates `org.jetbrains.kotlin:kotlin-allopen` 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](https://github.com/JetBrains/kotlin/compare/v2.1.20...v2.1.21)

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

@@ -1,5 +1,5 @@
 buildscript {
-	ext.kotlinVersion = '2.1.20'
+	ext.kotlinVersion = '2.1.21'
 	ext.isCI = System.getenv('GITHUB_ACTION')
 	repositories {
 		gradlePluginPortal()