Update lxml to 5.3.1

[pyup-bot]

This PR updates lxml from 5.3.0 to 5.3.1.

Changelog

5.3.1

==================

Bugs fixed
----------

* GH440: Some tests were adapted for libxml2 2.14.0.
Patch by Nick Wellnhofer.

* LP2097175: ``DTD(external_id="…")`` erroneously required a byte string as ID value.

* GH450: ``iterparse()`` internally triggered the `DeprecationWarning`` added in lxml 5.3.0 when parsing HTML.

Other changes
-------------

* GH442: Binary wheels for macOS no longer use the linker flag ``-flat_namespace``.

Links

• PyPI: https://pypi.org/project/lxml
• Changelog: https://data.safetycli.com/changelogs/lxml/
• Homepage: https://lxml.de/