invoke SystemHooksService instead of direct model

app/models/project.rb

@@ -975,9 +975,7 @@ class Project < ActiveRecord::Base
       end
     end
-    SystemHook.public_send(hooks_scope).each do |hook| # rubocop:disable GitlabSecurity/PublicSend
-      hook.async_execute(data, hooks_scope.to_s)
-    end
+    SystemHooksService.new.execute_hooks(data, hooks_scope)
   end
   def execute_services(data, hooks_scope = :push_hooks)

spec/models/project_spec.rb

@@ -3190,14 +3190,10 @@ describe Project do
     end
     it 'executes the system hooks with the specified scope' do
-      create :system_hook, merge_requests_events: true, tag_push_events: false
-      create :system_hook, merge_requests_events: false, tag_push_events: true
-      allow_any_instance_of(SystemHook).to receive(:async_execute).once
-      project = create :project
-      expect_any_instance_of(SystemHook).to receive(:async_execute).once
-
-      project.execute_hooks({}, :tag_push_hooks)
+      expect_any_instance_of(SystemHooksService).to receive(:execute_hooks).with({ data: 'data' }, :merge_request_hooks)
+      project = build(:project)
+      project.execute_hooks({ data: 'data' }, :merge_request_hooks)
     end
   end
 end