fix(users_controller_spec): Stub author permissions

The alchemy admin base controller now has a timezone
feature, which checks the user to have at least author
permissions (`:edit_content`). We need to stub this as well
because we stub `can? :update_user` in this spec as well.

Author: tvdeyen

spec/controllers/admin/users_controller_spec.rb

@@ -176,6 +176,10 @@ module Alchemy
 
       context "if user is permitted to update roles" do
         before do
+          allow(controller)
+            .to receive(:can?)
+            .with(:edit_content, Alchemy::Page)
+            .and_return(true)
           allow(controller)
             .to receive(:can?)
             .with(:update_role, Alchemy::User)
@@ -192,6 +196,10 @@ module Alchemy
 
       context "if the user is not permitted to update roles" do
         before do
+          allow(controller)
+            .to receive(:can?)
+            .with(:edit_content, Alchemy::Page)
+            .and_return(true)
           allow(controller)
             .to receive(:can?)
             .with(:update_role, Alchemy::User)