unpin lxml in edx-platform

[huniafatima-99]

lxml is pinned at lxml<5.0. lxml>=5.0 introduced breaking changes related to system dependencies
lxml==5.2.1 introduced new extra so we'll nee to rename lxml --> lxml[html-clean]
We have upgraded to python 3.12 so we can investigate and remove this constraint

[mfarhan943]

Unpinning the lxml constraint causes test failures due to a segmentation fault.

[feanil]

This seems to be resolved via #35272

When both libxmlsce and lxml were updated in tandem, we did not see the segfault issue.

[BilalQamar95]

Resolved via #35713

[feanil]

#35713 has now merged, this is now resolved.