Silence unused variable warning with php 8.3

    src/sp_unserialize.c: In function 'zif_sp_unserialize':
    src/sp_unserialize.c:131:15: warning: unused variable 'orig_handler' [-Wunused-variable]
      131 |   zif_handler orig_handler = zend_hash_str_find_ptr(SPG(sp_internal_functions_hook), ZEND_STRL("unserialize"));
          |               ^~~~~~~~~~~~

src/sp_unserialize.c

@@ -128,7 +128,9 @@ PHP_FUNCTION(sp_unserialize) {
     }
   } else { status = 1; }
 
+#if ! (PHP_VERSION_ID >= 80300)
   zif_handler orig_handler = zend_hash_str_find_ptr(SPG(sp_internal_functions_hook), ZEND_STRL("unserialize"));
+#endif
   if (0 == status) {
 #if PHP_VERSION_ID >= 80300
       // PHP8.3 gives a warning about trailing data in unserialize strings.