fix: unpin lxml constraint

[irtazaakram]

• Related to Study and fix crash on updating lxml==5.1.0 xblock-sdk#347

Fixes Error

E   ImportError: lxml.html.clean module is now a separate project lxml_html_clean.
E   Install lxml[html_clean] or lxml_html_clean directly.

E       AttributeError: 'TestConverter' object has no attribute 'assertEquals'. Did you mean: 'assertEqual'?

E       AttributeError: 'TestTransifex' object has no attribute 'assertRegexpMatches'

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

❗ No coverage uploaded for pull request base (master@2ae3902). Click here to learn what that means.

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #146   +/-   ##
=========================================
  Coverage          ?   99.78%           
=========================================
  Files             ?       11           
  Lines             ?      461           
  Branches          ?       33           
=========================================
  Hits              ?      460           
  Misses            ?        0           
  Partials          ?        1           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.