Bump kotlin.version from 1.9.20 to 1.9.21 in /samples/jvm/maven

Bumps `kotlin.version` from 1.9.20 to 1.9.21.

Updates `org.jetbrains.kotlin:kotlin-stdlib-jdk8` 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)

Updates `org.jetbrains.kotlin:kotlin-reflect` 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)

Updates `org.jetbrains.kotlin:kotlin-maven-plugin` from 1.9.20 to 1.9.21

---
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-maven-plugin
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

samples/jvm/maven/pom.xml

@@ -16,7 +16,7 @@
         <java.version>11</java.version>
         <junit.version>5.10.1</junit.version>
         <kotlin.compiler.jvmTarget>${java.version}</kotlin.compiler.jvmTarget>
-        <kotlin.version>1.9.20</kotlin.version>
+        <kotlin.version>1.9.21</kotlin.version>
         <maven-compiler-plugin.version>3.11.0</maven-compiler-plugin.version>
         <maven-surefire-plugin.version>3.2.2</maven-surefire-plugin.version>
         <project.build.sourceEncoding>${java.charset}</project.build.sourceEncoding>