The authentication check modal dialog appears just once

[afercia]

Noticed while investigating on #34951. To reproduce:

1. edit a post
2. open a new tab, go in some other admin screen and log out
3. in the tab with the edit post screen, after a while the authentication modal dialog appears
4. login again using the modal dialog
5. repeat step 2

The authentication modal dialog won't appear again because, as far as I see, when it gets hidden the custom event that triggers the dialog gets removed. See hide() in /wp-includes/js/wp-auth-check.js

$(document).off( 'heartbeat-tick.wp-auth-check' );

Not sure why the event is removed.

[walbo]

The patch fixes so the modal dialog appear again after second logout. Still removes the event if you close the modal by clicking the close button.