HTTP API: Improve docs for `wp_remote_retrieve_header` function return value.

This change updates the `@return` docs for `wp_remote_retrieve_header` to specify that an array can also be returned if the requested header key has multiple values.

Props robtarr, johnjamesjacoby, felipeelia, hellofromTonya, costdev.
Fixes #51736.
Built from https://develop.svn.wordpress.org/trunk@52441


git-svn-id: http://core.svn.wordpress.org/trunk@52033 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/http.php

@@ -222,7 +222,8 @@ function wp_remote_retrieve_headers( $response ) {
  *
  * @param array|WP_Error $response HTTP response.
  * @param string         $header   Header name to retrieve value from.
- * @return string The header value. Empty string on if incorrect parameter given, or if the header doesn't exist.
+ * @return array|string The header(s) value(s). Array if multiple headers with the same name are retrieved.
+ *                      Empty string if incorrect parameter given, or if the header doesn't exist.
  */
 function wp_remote_retrieve_header( $response, $header ) {
 	if ( is_wp_error( $response ) || ! isset( $response['headers'] ) ) {

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-beta4-52440';
+$wp_version = '5.9-beta4-52441';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.