Bump kotlin-gradle-plugin from 1.3.72 to 1.6.21

Bumps [kotlin-gradle-plugin](https://github.com/JetBrains/kotlin) from 1.3.72 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](https://github.com/JetBrains/kotlin/compare/v1.3.72...v1.6.21)

---
updated-dependencies:
- dependency-name: org.jetbrains.kotlin:kotlin-gradle-plugin
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

settings.gradle

@@ -8,7 +8,7 @@ buildscript {
 
     dependencies {
         //noinspection DifferentKotlinGradleVersion
-        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:1.3.72"
+        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:1.6.21"
         classpath "gradle.plugin.com.hierynomus.gradle.plugins:license-gradle-plugin:0.16.1"
         classpath "io.freefair.gradle:lombok-plugin:6.4.3"
     }