Bump kotlin.version from 2.0.20 to 2.0.21

Bumps `kotlin.version` 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-test` 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-maven-plugin` from 2.0.20 to 2.0.21

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

Signed-off-by: dependabot[bot] <[email protected]>

testsuite/extra/pom.xml

@@ -30,7 +30,7 @@
   <name>SmallRye Config: Test Suite - Extra</name>
 
   <properties>
-    <kotlin.version>2.0.20</kotlin.version>
+    <kotlin.version>2.0.21</kotlin.version>
   </properties>
 
   <dependencies>