build(deps): bump kotlin.version from 1.8.20 to 1.8.21 (#137)

Bumps `kotlin.version` from 1.8.20 to 1.8.21.

Updates `kotlin-stdlib-jdk8` from 1.8.20 to 1.8.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.8.20...v1.8.21)

Updates `kotlin-reflect` from 1.8.20 to 1.8.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.8.20...v1.8.21)

Updates `kotlin-test-junit` from 1.8.20 to 1.8.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/master/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.8.20...v1.8.21)

Updates `kotlin-maven-plugin` from 1.8.20 to 1.8.21

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib-jdk8
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-reflect
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-test-junit
  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] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

pom.xml

@@ -10,7 +10,7 @@
     <url>https://github.com/navikt/kafka-embedded-env</url>
 
     <properties>
-        <kotlin.version>1.8.20</kotlin.version>
+        <kotlin.version>1.8.21</kotlin.version>
         <kafka.version>3.2.3</kafka.version>
         <ktor.version>2.3.0</ktor.version>
         <confluent.version>7.3.1</confluent.version>