build(deps): bump kotlin.version from 1.6.20 to 1.6.21 (#353)

Bumps `kotlin.version` from 1.6.20 to 1.6.21.

Updates `kotlin-stdlib` from 1.6.20 to 1.6.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.6.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.6.20...v1.6.21)

Updates `kotlin-stdlib-jdk7` from 1.6.20 to 1.6.21
- [Release notes](https://github.com/JetBrains/kotlin/releases)
- [Changelog](https://github.com/JetBrains/kotlin/blob/v1.6.21/ChangeLog.md)
- [Commits](JetBrains/kotlin@v1.6.20...v1.6.21)

Updates `kotlin-maven-plugin` from 1.6.20 to 1.6.21

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib
  dependency-type: direct:production
  update-type: version-update:semver-patch
- dependency-name: org.jetbrains.kotlin:kotlin-stdlib-jdk7
  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] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

plc4j/examples/hello-world-kotlin/pom.xml

@@ -32,7 +32,7 @@
   <name>PLC4J: Examples: Hello-World: Kotlin</name>
 
   <properties>
-    <kotlin.version>1.6.20</kotlin.version>
+    <kotlin.version>1.6.21</kotlin.version>
     <kotlin.compiler.incremental>true</kotlin.compiler.incremental>
     <junit-jupiter.version>5.8.2</junit-jupiter.version>
     <app.main.class>org.apache.plc4x.java.examples.hellokotlin.ReadModbusPalKt</app.main.class>

plc4j/integrations/apache-calcite/pom.xml

@@ -185,12 +185,12 @@
       <dependency>
         <groupId>org.jetbrains.kotlin</groupId>
         <artifactId>kotlin-stdlib</artifactId>
-        <version>1.6.20</version>
+        <version>1.6.21</version>
       </dependency>
       <dependency>
         <groupId>org.jetbrains.kotlin</groupId>
         <artifactId>kotlin-stdlib-jdk7</artifactId>
-        <version>1.6.20</version>
+        <version>1.6.21</version>
       </dependency>
       <dependency>
         <groupId>org.jetbrains.kotlin</groupId>