Bump org.jetbrains.dokka:dokka-gradle-plugin from 1.6.10 to 1.9.20

Bumps [org.jetbrains.dokka:dokka-gradle-plugin](https://github.com/Kotlin/dokka) from 1.6.10 to 1.9.20.
- [Release notes](https://github.com/Kotlin/dokka/releases)
- [Commits](Kotlin/dokka@v1.6.10...v1.9.20)

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

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

build.gradle

@@ -2,7 +2,7 @@
 
 buildscript {
     ext.kotlin_version = '1.8.21'
-    ext.dokka_version = '1.6.10'
+    ext.dokka_version = '1.9.20'
 
     ext {
         group = 'com.github.markusressel'