[Fleet] Fix warning icon not displaying on 8.7

With EUI v76, `warning` icon type was introduced: #152506

However, the EUI upgrade was only applied on 8.8. The callout here that uses the warning icon was backported to 8.7, where the EUI version does not have the `warning` icon type. Thus 8.7 should still use the legacy `alert` icon type.

This PR fixes that and will only be merged into 8.7.

x-pack/plugins/fleet/public/applications/fleet/sections/settings/components/edit_output_flyout/confirm_update.tsx

@@ -67,7 +67,7 @@ const ConfirmDescription: React.FunctionComponent<ConfirmDescriptionProps> = ({
       <>
         <EuiSpacer size="s" />
         <EuiCallOut
-          iconType="warning"
+          iconType="alert"
           color="warning"
           size="m"
           title={