chore(deps): bump kotlin in /samples/kotlin-mcp-server

Bumps `kotlin` from 2.2.21 to 2.3.20.

Updates `org.jetbrains.kotlin.jvm` from 2.2.21 to 2.3.20
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.2.21...v2.3.20)

Updates `org.jetbrains.kotlin.plugin.serialization` from 2.2.21 to 2.3.20
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v2.2.21...v2.3.20)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin.jvm
  dependency-version: 2.3.20
  dependency-type: direct:production
  update-type: version-update:semver-minor
- dependency-name: org.jetbrains.kotlin.plugin.serialization
  dependency-version: 2.3.20
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

samples/kotlin-mcp-server/gradle/libs.versions.toml

@@ -1,5 +1,5 @@
 [versions]
-kotlin = "2.2.21"
+kotlin = "2.3.20"
 ktor = "3.3.3"
 mcp-kotlin = "0.10.0"
 slf4j = "2.0.17"