Merge hashes to de-dupe the app and role envs.

This is better then adding them together which confusingly results in
both ENV vars in the same file, though based on the load order, they
worked anyway.

lib/kamal/configuration/role.rb

@@ -239,7 +239,7 @@ class Kamal::Configuration::Role
         clear_app_env  = config.env["secret"] ? Array(config.env["clear"]) : Array(config.env["clear"] || config.env)
         clear_role_env = specialized_env["secret"] ? Array(specialized_env["clear"]) : Array(specialized_env["clear"] || specialized_env)
 
-        new_env["clear"] = (clear_app_env + clear_role_env).uniq
+        new_env["clear"] = clear_app_env.to_h.merge(clear_role_env.to_h)
       end
     end