DEV: Fix flaky specs (#13226)

Some specs failed when `LOAD_PLUGINS=1` was set while migrating the test DB and the narrative-bot plugin disabled the `send_welcome_message` site setting.

spec/requests/users_controller_spec.rb

@@ -64,6 +64,7 @@ describe UsersController do
     context 'valid token' do
       context 'welcome message' do
         it 'enqueues a welcome message if the user object indicates so' do
+          SiteSetting.send_welcome_message = true
           user.update(active: false)
           put "/u/activate-account/#{token}"
           expect(response.status).to eq(200)