Set response code for ads.txt requests (#14174)

Under some configurations, the web server will set a status code of 404 for requests to domain.com/ads.txt since the physical file cannot be present for WordAds to return an automatically generated ads.txt. When the generated response is sent, no response code was set so the previous 404 is used. This will cause crawlers such as Google's to ignore the response and the file will be considered non-existent.

Fixes #14169

modules/wordads/wordads.php

@@ -174,6 +174,7 @@ function init() {
 			 */
 			$ads_txt_content = apply_filters( 'wordads_ads_txt', $ads_txt_transient );
 
+			http_response_code( 200 );
 			header( 'Content-Type: text/plain; charset=utf-8' );
 			echo esc_html( $ads_txt_content );
 			die();