Adding lxml to requirements_dev.txt
- [X ] closes #17747
- [X ] tests added / passed
- [X ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

can you add the skip where needed? Added @jreback, thanks for taking care of this. @TomAugspurger does this fix the original issue?

@datapythonista can you rebase @jreback, not sure if I'm missing anything, but I see the PR already rebased, isn't it? thanks @datapythonista 