Bump dokka-maven-plugin from 1.6.10 to 1.6.21

Bumps [dokka-maven-plugin](https://github.com/Kotlin/dokka) from 1.6.10 to 1.6.21.
- [Release notes](https://github.com/Kotlin/dokka/releases)
- [Commits](https://github.com/Kotlin/dokka/commits)

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

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

build-parent/pom.xml

@@ -21,7 +21,7 @@
         <!-- Quarkus uses jboss-parent and it comes with 3.8.1-jboss-1, we don't want that in the templates -->
         <compiler-plugin.version>3.8.1</compiler-plugin.version>
         <kotlin.version>1.6.21</kotlin.version>
-        <dokka.version>1.6.10</dokka.version>
+        <dokka.version>1.6.21</dokka.version>
         <scala.version>2.13.8</scala.version>
         <scala-maven-plugin.version>4.6.1</scala-maven-plugin.version>
         <!-- not pretty but this is used in the codestarts and we don't want to break compatibility -->