Bump kotlin from 2.1.20 to 2.1.21

Bumps `kotlin` from 2.1.20 to 2.1.21.

Updates `org.jetbrains.kotlin.multiplatform` 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.plugin.compose` 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.plugin.serialization` 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.multiplatform
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin.plugin.compose
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin.plugin.serialization
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

gradle/libs.versions.toml

@@ -1,6 +1,6 @@
 [versions]
 
-kotlin = "2.1.20"
+kotlin = "2.1.21"
 compose = "1.8.0"
 compose-hot-reload = "1.0.0-alpha09"
 agp = "8.7.3"