build(deps): bump lxml from 4.8.0 to 4.9.1 in /requirements

Bumps [lxml](https:/lxml/lxml) from 4.8.0 to 4.9.1.
- [Release notes](https:/lxml/lxml/releases)
- [Changelog](https:/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-4.8.0...lxml-4.9.1)

---
updated-dependencies:
- dependency-name: lxml
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements/base.txt

@@ -35,7 +35,7 @@ click-repl==0.2.0
  # via celery
 django==3.2.13
  # via
- # -c requirements/common_constraints.txt
+ # -c common_constraints.txt
  # django-crum
  # django-model-utils
  # djangorestframework
@@ -58,7 +58,7 @@ django-waffle==2.4.1
 djangorestframework==3.13.1
  # via super-csv
 edx-bulk-grades==1.0.0
- # via -r requirements/base.in
+ # via -r base.in
 edx-celeryutils==1.2.1
  # via super-csv
 edx-django-utils==5.0.0
@@ -71,18 +71,16 @@ future==0.18.2
  # via edx-celeryutils
 idna==3.3
  # via requests
-importlib-metadata==4.11.4
- # via markdown
 jsonfield==3.1.0
  # via edx-celeryutils
 kombu==5.2.4
  # via celery
-lxml==4.8.0
+lxml==4.9.1
  # via xblock
 mako==1.2.0
  # via xblock-utils
 markdown==3.3.7
- # via -r requirements/base.in
+ # via -r base.in
 markupsafe==2.1.1
  # via
  # mako
@@ -92,7 +90,7 @@ newrelic==7.10.0.175
 path==16.4.0
  # via path-py
 path-py==12.5.0
- # via -r requirements/base.in
+ # via -r base.in
 pbr==5.9.0
  # via stevedore
 prompt-toolkit==3.0.29
@@ -149,19 +147,17 @@ wcwidth==0.2.5
  # via prompt-toolkit
 web-fragments==2.0.0
  # via
- # -r requirements/base.in
+ # -r base.in
  # xblock
  # xblock-utils
 webob==1.8.7
  # via xblock
 xblock==1.6.1
  # via
- # -r requirements/base.in
+ # -r base.in
  # xblock-utils
 xblock-utils==3.0.0
- # via -r requirements/base.in
-zipp==3.8.0
- # via importlib-metadata
+ # via -r base.in
 
 # The following packages are considered to be unsafe in a requirements file:
 # setuptools