Try to fix libxml 2.9.12 tests

The test expectations here were for PHP 8.0, try to adjust them
for PHP 7.4.

Make tests compatible with libxml2 2.9.12

This version of libxml introduced quite a few changes. Most of
them are differences in error reporting, while some also change
behavior, e.g

Make tests compatible with libxml2 2.9.12

This version of libxml introduced quite a few changes. Most of
them are differences in error reporting, while some also change
behavior, e.g. null bytes are no longer supported and xinclude
recursion is limited.

Closes GH-7030. Closes GH-7046.

Co-authored-by: Nikita Popov <nikic@php.net>

show more ...