build(deps): bump org.jetbrains.kotlin:kotlin-gradle-plugin (#12)

Bumps [org.jetbrains.kotlin:kotlin-gradle-plugin](https://github.com/JetBrains/kotlin) from 1.9.20 to 1.9.21.
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.9.20...v1.9.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-gradle-plugin
  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

@@ -10,7 +10,7 @@ junit-api = { module = "org.junit.jupiter:junit-jupiter-api", version.ref = "jun
 junit-engine = { module = "org.junit.jupiter:junit-jupiter-engine", version.ref = "junit" }
 junit-params = { module = "org.junit.jupiter:junit-jupiter-params", version.ref = "junit" }
 plugin-android = "com.android.tools.build:gradle:8.1.1"
-plugin-kotlin = "org.jetbrains.kotlin:kotlin-gradle-plugin:1.9.20"
+plugin-kotlin = "org.jetbrains.kotlin:kotlin-gradle-plugin:1.9.21"
 
 [bundles]
 junit = ['junit-api', 'junit-params']