Fix build by disabling linking to JUnit 5.8.1 Javadoc

The `package-list` file no longer exists at
https://junit.org/junit5/docs/5.8.1/api/, due to the following commit.

67ad4e5455

build.gradle

@@ -384,7 +384,9 @@ configure([rootProject] + javaProjects) { project ->
 			"https://hc.apache.org/httpcomponents-client-5.1.x/current/httpclient5/apidocs/",
 			"https://projectreactor.io/docs/test/release/api/",
 			"https://junit.org/junit4/javadoc/4.13.2/",
-			"https://junit.org/junit5/docs/5.8.1/api/",
+			// Disabling linking to JUnit 5.8.1, since the `package-list` file no longer exists due to
+			// https://github.com/junit-team/junit5/commit/67ad4e545518b0ce2b0e7c96df31a669866d5003.
+			// "https://junit.org/junit5/docs/5.8.1/api/",
 			"https://www.reactive-streams.org/reactive-streams-1.0.3-javadoc/",
 			"https://javadoc.io/static/io.rsocket/rsocket-core/1.1.1/",
 			"https://r2dbc.io/spec/0.8.5.RELEASE/api/"