Fix StaleElementReferenceError and ensure `add_member` success

qa/qa/resource/members.rb

@@ -8,9 +8,12 @@ module QA
     #
     module Members
       def add_member(user, access_level = AccessLevel::DEVELOPER)
-        QA::Runtime::Logger.debug(%Q[Adding user #{user.username} to #{full_path} #{self.class.name}])
+        Support::Retrier.retry_until do
+          QA::Runtime::Logger.debug(%Q[Adding user #{user.username} to #{full_path} #{self.class.name}])
 
-        post Runtime::API::Request.new(api_client, api_members_path).url, { user_id: user.id, access_level: access_level }
+          response = post Runtime::API::Request.new(api_client, api_members_path).url, { user_id: user.id, access_level: access_level }
+          response.code == QA::Support::Api::HTTP_STATUS_CREATED
+        end
       end
 
       def remove_member(user)

qa/qa/support/wait_for_requests.rb

@@ -27,7 +27,10 @@ module QA
         # The number of selectors should be able to be reduced after
         # migration to the new spinner is complete.
         # https://gitlab.com/groups/gitlab-org/-/epics/956
-        Capybara.page.has_no_css?('.gl-spinner, .fa-spinner, .spinner', wait: wait)
+        # retry_on_exception added here due to `StaleElementReferenceError`. See: https://gitlab.com/gitlab-org/gitlab/-/issues/232485
+        Support::Retrier.retry_on_exception do
+          Capybara.page.has_no_css?('.gl-spinner, .fa-spinner, .spinner', wait: wait)
+        end
       end
     end
   end