Fix property 'at' does not exist error

Author: mukeshpanchal27

plugins/optimization-detective/detect.js

@@ -789,7 +789,7 @@ export default async function detect( {
 		elements: [],
 	};
 
-	const lcpMetric = lcpMetricCandidates.at( -1 );
+	const lcpMetric = lcpMetricCandidates[ lcpMetricCandidates.length - 1 ];
 
 	// Populate the elements in the URL Metric.
 	for ( const elementIntersection of elementIntersections ) {