[catalog_controller_spec.rb] Fix ems let... again

This is a follow up to 02e4b85 as the solution provided there, while
works for this use case, ended up causing problems in
`ManageIQ/manageiq-content`:

ManageIQ/manageiq#20787 (comment)

Instead, we use the :provider_embedded_ansible factory, and reference
the `.automation_manager` from that.  In addition, since a update to the
`:inventory_root_groups` was needed, we also modify the record in a
`before` statement as well.

This ends up not being as clean as the previous implementation, but
makes sure we are using the `EmbeddedAnsible` provider in the form that
it would be called when used in the application.

spec/controllers/catalog_controller_spec.rb

@@ -733,9 +733,8 @@
       let(:auth) { FactoryBot.create(:authentication, :manager_ref => 6, :type => "ManageIQ::Providers::EmbeddedAnsible::AutomationManager::MachineCredential") }
       let(:repository) { FactoryBot.create(:configuration_script_source, :manager => ems, :type => "ManageIQ::Providers::EmbeddedAnsible::AutomationManager::ConfigurationScriptSource") }
       let(:inventory_root_group) { FactoryBot.create(:inventory_root_group) }
-      let(:ems) do
-        FactoryBot.create(:embedded_automation_manager_ansible, :inventory_root_groups => [inventory_root_group])
-      end
+      let(:provider) { FactoryBot.create(:provider_embedded_ansible) }
+      let(:ems) { provider.automation_manager }
       let(:dialog) { FactoryBot.create(:dialog) }
       let(:playbook) do
         FactoryBot.create(:embedded_playbook,
@@ -744,6 +743,10 @@
                            :inventory_root_group        => inventory_root_group)
       end
 
+      before do
+        ems.update_attributes(:inventory_root_groups => [inventory_root_group])
+      end
+
       it "returns playbook service template details for provision & retirement tabs for summary screen" do
         options = {
           :name        => 'test_ansible_catalog_item',