chore(deps): Bump kotlinVersion from 2.0.20 to 2.0.21

Bumps `kotlinVersion` from 2.0.20 to 2.0.21.

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)

Updates `org.jetbrains.kotlin.plugin.serialization` 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.jvm
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin.plugin.serialization
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

springwolf-add-ons/springwolf-kotlinx-serialization-model-converter/build.gradle

@@ -1,6 +1,6 @@
 buildscript {
     ext {
-        kotlinVersion = '2.0.20'
+        kotlinVersion = '2.0.21'
         kotlinxSerializationVersion = '1.7.2'
     }
 }