Bump kotlin.version from 2.1.20 to 2.1.21 (#1553)

Bumps `kotlin.version` from 2.1.20 to 2.1.21.

Updates `org.jetbrains.kotlin:kotlin-stdlib-jdk8` 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](JetBrains/kotlin@v2.1.20...v2.1.21)

Updates `org.jetbrains.kotlin:kotlin-test` 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](JetBrains/kotlin@v2.1.20...v2.1.21)

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

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib-jdk8
  dependency-version: 2.1.21
  dependency-type: direct:development
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-test
  dependency-version: 2.1.21
  dependency-type: direct:development
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-maven-plugin
  dependency-version: 2.1.21
  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>

Author: dependabot[bot]

pom.xml

@@ -54,7 +54,7 @@
         <!-- Run tests in Turkish to make sure that they don't depend on
                          locale. Turkish is a notoriously tricky locale. -->
         <surefire.argline>@{argLine} -Duser.language=TR -Duser.country=tr</surefire.argline>
-        <kotlin.version>2.1.20</kotlin.version>
+        <kotlin.version>2.1.21</kotlin.version>
     </properties>
     <licenses>
         <license>