Bump lxml from 4.4.0 to 4.6.2

Bumps [lxml](https://github.com/lxml/lxml) from 4.4.0 to 4.6.2.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-4.4.0...lxml-4.6.2)

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

requirements-optional.txt

@@ -2,7 +2,7 @@ Cython<0.29.21,>=0.29.13
 numpy<=1.19.2,>=1.16.4
 numexpr<=2.7.1,>=2.6.9
 intervaltree==3.0.2
-lxml==4.4.0
+lxml==4.6.2
 openpyxl==2.6.2
 pandas<=1.1.2,>=0.24.2 ; python_version < '3.9'
 PyMySQL==0.9.3