Bump kotlin from 2.0.20 to 2.0.21 (#42)

Bumps `kotlin` from 2.0.20 to 2.0.21.

Updates `org.jetbrains.kotlin:kotlin-test` 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.multiplatform` 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:kotlin-test
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin.multiplatform
  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] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

gradle/libs.versions.toml

@@ -1,6 +1,6 @@
 [versions]
 agp = "8.7.0"
-kotlin = "2.0.20"
+kotlin = "2.0.21"
 nexus-publish = "2.0.0"
 kotlinx-serialization = "1.7.3"
 kotlinx-datetime = "0.6.1"