fix stock status is not correct in JSON structure data if product is onbackorder

plugins/woocommerce/changelog/fix-28214

@@ -0,0 +1,4 @@
+Significance: patch
+Type: fix
+
+fix stock status is not correct in JSON structure data if product is onbackorder

plugins/woocommerce/includes/class-wc-structured-data.php

@@ -257,9 +257,25 @@ class WC_Structured_Data {
 				);
 			}
 
+            $stock_status = $product->get_stock_status();
+
+            switch ( $stock_status ) {
+                case "instock":
+                    $stock_status_schema = "InStock";
+                    break;
+                case "outofstock":
+                    $stock_status_schema = "OutOfStock";
+                    break;
+                case "onbackorder":
+                    $stock_status_schema = "BackOrder";
+                    break;
+                default:
+                    $stock_status_schema = "";
+            }
+
 			$markup_offer += array(
 				'priceCurrency' => $currency,
-				'availability'  => 'http://schema.org/' . ( $product->is_in_stock() ? 'InStock' : 'OutOfStock' ),
+				'availability'  => 'http://schema.org/' . $stock_status_schema,
 				'url'           => $permalink,
 				'seller'        => array(
 					'@type' => 'Organization',