Bump kotlin from 1.8.20 to 1.8.21

Bumps `kotlin` from 1.8.20 to 1.8.21.

Updates `org.jetbrains.kotlin:kotlin-gradle-plugin` from 1.8.20 to 1.8.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.8.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.8.20...v1.8.21)

Updates `org.jetbrains.kotlin.android` from 1.8.20 to 1.8.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.8.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.8.20...v1.8.21)

Updates `org.jetbrains.kotlin.plugin.serialization` from 1.8.20 to 1.8.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.8.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.8.20...v1.8.21)

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

gradle/libs.versions.toml

@@ -10,7 +10,7 @@ target-sdk = "33"
 # @pin
 gradle = "8.0.0"
 # @pin update when updating compose compiler
-kotlin = "1.8.20"
+kotlin = "1.8.21"
 kotlin-ksp = "1.8.20-1.0.11"
 kotlin-coroutines = "1.6.4"
 kotlin-serialization = "1.5.0"