fix: heading anchor id
When pointing to anchors via `some.adoc#anchor` either naming the anchor or making sure that the generated anchor ID is used prevents us from creating broken links.
See:
@@ -45,7 +45,7 @@ A build with integration tests in both the JVM mode and the native mode:
$ mvn clean install -Pnative
----
-
+[[create-a-new-extension]]
== Create a new extension
1. You should know link:#how-to-build[how to build].
