How to create an alert with only severity "critical" and "warning" label in OpenShift 4

Issue

• How to create a receiver that notifies alerts with critical and warning severity labels in Alertmanager?
• I ｗant to receive notifications via email that an alert with severity labels critical and warning fired. There is no need to separate the recipients for each severity and to simplify the maintenance of the configuration, I want to set up a single receiver.
• If I set severity=critical and severity=warning labels to "Routing labels" in the receiver creation menu, the label names must be unique and cannot be created.
  
• Do I have to create a receiver for each severity label, even for a single notification destination?