Update dependency org.jetbrains.dokka to v1.6.21

| datasource | package                                               | from  | to     |
| ---------- | ----------------------------------------------------- | ----- | ------ |
| maven      | org.jetbrains.dokka:org.jetbrains.dokka.gradle.plugin | 1.6.0 | 1.6.21 |

gradle/projects.libs.versions.toml

@@ -4,7 +4,7 @@ arrowGradleConfig = "0.10.0"
 arrowAnalysis = "2.0.2-SNAPSHOT"
 assertj = "3.22.0"
 classgraph = "4.8.143"
-dokka = "1.6.0"
+dokka = "1.6.21"
 intellijOpenApi = "7.0.3"
 javaAssist = "3.28.0-GA"
 junit = "5.8.2"