Bump lxml from 4.6.5 to 4.7.1 (#173)

Bumps [lxml](https://github.com/lxml/lxml) from 4.6.5 to 4.7.1.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-4.6.5...lxml-4.7.1)

---
updated-dependencies:
- dependency-name: lxml
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements_dev.txt

@@ -2,7 +2,7 @@ Sphinx==4.3.1
 black==21.12b0
 coverage==6.2
 flake8==4.0.1
-lxml==4.6.5
+lxml==4.7.1
 mypy==0.910
 pylint==2.12.2
 pytest==6.2.5