Bump org.jetbrains.dokka:dokka-gradle-plugin from 1.8.20 to 1.9.20

Bumps [org.jetbrains.dokka:dokka-gradle-plugin](https://github.com/Kotlin/dokka) from 1.8.20 to 1.9.20.
- [Release notes](https://github.com/Kotlin/dokka/releases)
- [Commits](Kotlin/dokka@v1.8.20...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] <support@github.com>

buildSrc/build.gradle.kts

@@ -9,7 +9,7 @@ repositories {
 }
 
 dependencies {
-    implementation("org.jetbrains.dokka:dokka-gradle-plugin:1.8.20")
+    implementation("org.jetbrains.dokka:dokka-gradle-plugin:1.9.20")
     implementation("de.undercouch:gradle-download-task:5.6.0")
 
 }