Update lxml requirement from ~=5.3.2 to ~=5.4.0

Updates the requirements on [lxml](https://github.com/lxml/lxml) to permit the latest version.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-5.3.2...lxml-5.4.0)

---
updated-dependencies:
- dependency-name: lxml
  dependency-version: 5.4.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -8,7 +8,7 @@ docutils~=0.21.2
 idna~=3.10
 imagesize~=1.4.1
 Jinja2~=3.1.6
-lxml~=5.3.2
+lxml~=5.4.0
 m2r2~=0.3.3.post2
 MarkupSafe~=3.0.2
 mistune~=0.8.4