Bump org.jetbrains.kotlin:kotlin-gradle-plugin from 1.6.10 to 1.6.21

Bumps [org.jetbrains.kotlin:kotlin-gradle-plugin](https://github.com/JetBrains/kotlin) from 1.6.10 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@v1.6.10...v1.6.21)

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

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

Author: dependabot[bot]

buildSrc/build.gradle

@@ -22,7 +22,7 @@ dependencies {
 	implementation "io.spring.nohttp:nohttp-gradle:0.0.11"
 	implementation "org.asciidoctor:asciidoctor-gradle-jvm:3.3.2"
 	implementation "org.asciidoctor:asciidoctor-gradle-jvm-pdf:3.3.2"
-	implementation "org.jetbrains.kotlin:kotlin-gradle-plugin:1.6.10"
+	implementation "org.jetbrains.kotlin:kotlin-gradle-plugin:1.6.21"
 	implementation "org.hidetake:gradle-ssh-plugin:2.10.1"
 	implementation "org.jfrog.buildinfo:build-info-extractor-gradle:5.2.0"
 	implementation "org.sonarsource.scanner.gradle:sonarqube-gradle-plugin:2.7.1"