chore(deps): bump urllib3 from 1.26.16 to 1.26.18 in /requirements

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.16 to 1.26.18.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.26.16...1.26.18)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-type: direct:production
...

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

requirements/edx-platform-constraints.txt

@@ -1134,7 +1134,7 @@ uritemplate==4.1.1
     # via
     #   coreapi
     #   drf-yasg
-urllib3==1.26.16
+urllib3==1.26.18
     # via
     #   -c requirements/edx/../constraints.txt
     #   -r requirements/edx/paver.txt