Upgrade to antora-ui-spring 0.4.12

Author: sdeleuze

antora-playbook.yml

@@ -43,5 +43,5 @@ runtime:
     failure_level: warn
 ui:
   bundle:
-    url: https://github.com/spring-io/antora-ui-spring/releases/download/v0.4.9/ui-bundle.zip
+    url: https://github.com/spring-io/antora-ui-spring/releases/download/v0.4.12/ui-bundle.zip
     snapshot: true