Update compatible versions of lxml

No breaking changes which affect us have been introduced.

Author: WhyNotHugo

pyproject.toml

@@ -31,7 +31,7 @@ dependencies = [
   "cryptography>=3.2,<47",
   "django>=5.2,<6.1",
   "django_renderpdf>=6.0.0,<7.0.0",
-  "lxml>=3.4.4",
+  "lxml<7.0.0",
   "pyopenssl>=16.2.0",
   "setuptools-git>=1.1",
   "wheel>=0.24.0",