fix: avoid engine options mutation on mount (#3783)

Author: Paul-Bob

Diff for: lib/avo/engine.rb

@@ -70,7 +70,7 @@ def mount_avo(at: Avo.configuration.root_path, **options)
 
           scope at do
             Avo.plugin_manager.engines.each do |engine|
-              mount engine[:klass], **engine[:options]
+              mount engine[:klass], **engine[:options].dup
             end
           end
         end