Last search request to return displays in post selector

[dlh01]

Description of the bug

Somewhat related to #152: If the post selector makes multiple requests to the search endpoint, the last of those requests to return will be the one whose results are displayed, even if it wasn't the last request that was actually sent for the current search term.

Steps To Reproduce

Add this snippet somewhere:

if ( 'par' === ( $_GET['search'] ?? '' ) ) {
	sleep( 5 );
}

Open the post selector and the Network tab of your browser tools. Search for park in the post selector (or use a different word that works better with your test data). You should see search requests for par and park.

The request for park will return first and populate the selector results. The request for par returns second, and the results for that search will replace the results that were there for park.

Additional Information

No response