chore(deps): bump kotlin from 2.2.20 to 2.2.21

Bumps `kotlin` from 2.2.20 to 2.2.21.

Updates `org.jetbrains.kotlin:kotlin-test` from 2.2.20 to 2.2.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.2.20...v2.2.21)

Updates `org.jetbrains.kotlin.multiplatform` from 2.2.20 to 2.2.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.2.20...v2.2.21)

Updates `org.jetbrains.kotlin.plugin.serialization` from 2.2.20 to 2.2.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.2.20...v2.2.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-test
  dependency-version: 2.2.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin.multiplatform
  dependency-version: 2.2.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin.plugin.serialization
  dependency-version: 2.2.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

gradle/libs.versions.toml

@@ -2,7 +2,7 @@
 agp = "8.13.0"
 clikt = "5.0.3"
 flexMessagingCore = "4.8.0"
-kotlin = "2.2.20"
+kotlin = "2.2.21"
 dokka = "2.0.0"
 kotlinxCoroutines = "1.10.2"
 kotlinxDatetime = "0.7.1"