Update Dokka to 1.9.20 (#4057)

Author: whyoleg

gradle.properties

@@ -11,7 +11,7 @@ junit5_version=5.7.0
 knit_version=0.5.0
 html_version=0.7.2
 lincheck_version=2.18.1
-dokka_version=1.9.10
+dokka_version=1.9.20
 byte_buddy_version=1.10.9
 reactor_version=3.4.1
 reactive_streams_version=1.0.3