Bump kotlin from 2.0.21 to 2.1.21

Bumps `kotlin` from 2.0.21 to 2.1.21.

Updates `org.jetbrains.kotlin:kotlin-bom` from 2.0.21 to 2.1.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.0.21...v2.1.21)

Updates `org.jetbrains.kotlin.jvm` from 2.0.21 to 2.1.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.0.21...v2.1.21)

Updates `org.jetbrains.kotlin.plugin.serialization` from 2.0.21 to 2.1.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.0.21...v2.1.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-bom
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.jetbrains.kotlin.jvm
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.jetbrains.kotlin.plugin.serialization
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

gradle/libs.versions.toml

@@ -1,5 +1,5 @@
 [versions]
-kotlin = "2.0.21"
+kotlin = "2.1.21"
 ktor = "2.3.12"
 hoplite = "2.9.0"
 kondor = "3.2.3"