Update dependency org.jetbrains.dokka:dokka-gradle-plugin to v1.8.20

Author: renovate[bot]

buildSrc/build.gradle.kts

@@ -36,7 +36,7 @@ dependencies {
     implementation("org.jetbrains.kotlinx:kotlinx-benchmark-plugin:0.4.7")
     implementation("org.jetbrains.kotlinx:atomicfu-gradle-plugin:0.18.5")
     implementation("com.diffplug.spotless:spotless-plugin-gradle:6.12.0")
-    implementation("org.jetbrains.dokka:dokka-gradle-plugin:1.7.20")
+    implementation("org.jetbrains.dokka:dokka-gradle-plugin:1.8.20")
     implementation("dev.floofy.commons:gradle:2.4.1")
     implementation(kotlin("serialization", "1.7.22"))
     implementation(kotlin("gradle-plugin", "1.7.22"))