Add missing Content-Type headers in test files.

Author: amouhzi

tests/server/php-curl-test/post_file_path_upload.php

@@ -18,4 +18,6 @@
     $response['mime_content_type'] = 'ERROR';
 }
 
+header('Content-Type: application/json');
+
 echo json_encode($response);

tests/server/php-curl-test/post_multidimensional.php

@@ -1,4 +1,7 @@
 <?php
 
 $http_raw_post_data = file_get_contents('php://input');
+
+header('Content-Type: text/plain');
+
 echo $http_raw_post_data;