build(deps): bump kotlin from 2.0.20 to 2.0.21 (#727)

Bumps `kotlin` from 2.0.20 to 2.0.21.

Updates `org.jetbrains.kotlin:kotlin-stdlib-jdk8` 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:kotlin-reflect` 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-stdlib-jdk8
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-reflect
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

gradle/libs.versions.toml

@@ -1,6 +1,6 @@
 [versions]
 micronautPlatform = "4.6.3"
-kotlin = "2.0.20"
+kotlin = "2.0.21"
 jackson = "2.18.0"
 kotest = "5.9.1"