[Security] Bump urllib3 from 1.26.3 to 1.26.4

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.3 to 1.26.4. **This update includes a security fix.**
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](https://github.com/urllib3/urllib3/compare/1.26.3...1.26.4)

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

requirements/dev.txt

diff --git a/requirements/dev.txt b/requirements/dev.txt
index 218acf3..11413bc 100644
--- a/requirements/dev.txt
+++ b/requirements/dev.txt
@@ -117,7 +117,7 @@
     # via mypy
 typing-extensions==3.7.4.3
     # via mypy
-urllib3==1.26.3
+urllib3==1.26.4
     # via requests
 virtualenv==20.4.2
     # via

requirements/docs.txt

diff --git a/requirements/docs.txt b/requirements/docs.txt
index 2303671..1f7c3d9 100644
--- a/requirements/docs.txt
+++ b/requirements/docs.txt
@@ -60,7 +60,7 @@
     # via sphinx
 sphinxcontrib-serializinghtml==1.1.4
     # via sphinx
-urllib3==1.26.3
+urllib3==1.26.4
     # via requests
 
 # The following packages are considered to be unsafe in a requirements file: