fix: allow to use lxml < 6.1.0 so it works with libxml2 2.15

[fabien-michel]

I've ran tests with libxml2 2.15 and python 3.12, 3.13 and 3.14.

I didn't try with libxml2 2.14.

Closes #102

With this patch, one can force lxml to 6.0.2 in dependencies.

[tool.poetry.dependencies]
inscriptis = "~=2.7.0"
lxml = ">=6.0.2"