Adjust skip list for moved test

The two remaining test_old failures are due to a bug on the PHP
side.

Author: nikic

test_old/run.php

@@ -101,6 +101,7 @@ function showHelp($error) {
 | Zend.tests.bug74947
 # pretty print differences due to negative LNumbers
 | Zend.tests.neg_num_string
+| Zend.tests.numeric_strings.neg_num_string
 | Zend.tests.bug72918
 # pretty print difference due to nop statements
 | ext.mbstring.tests.htmlent