build(deps): bump kotlin.version from 2.1.20 to 2.1.21

Bumps `kotlin.version` from 2.1.20 to 2.1.21.

Updates `org.jetbrains.kotlin:kotlin-maven-plugin` from 2.1.20 to 2.1.21

Updates `org.jetbrains.kotlin:kotlin-stdlib` from 2.1.20 to 2.1.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/commits)

Updates `org.jetbrains.kotlin:kotlin-stdlib-common` from 2.1.20 to 2.1.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/commits)

Updates `org.jetbrains.kotlin:kotlin-test-junit` from 2.1.20 to 2.1.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](https://github.com/JetBrains/kotlin/commits)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-maven-plugin
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib-common
  dependency-version: 2.1.21
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-test-junit
  dependency-version: 2.1.21
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

pom.xml

@@ -117,7 +117,7 @@
         <maven-compiler-plugin.release>17</maven-compiler-plugin.release>
 
         <!-- Configuration of mutiny-kotlin module -->
-        <kotlin.version>2.1.20</kotlin.version>
+        <kotlin.version>2.1.21</kotlin.version>
         <kotlin.compiler.apiVersion>1.8</kotlin.compiler.apiVersion>
         <kotlin.compiler.languageVersion>1.8</kotlin.compiler.languageVersion>
         <coroutines.version>1.10.2</coroutines.version>