Bump urllib3 from 1.26.4 to 1.26.5 in /backend

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.4 to 1.26.5.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.26.4...1.26.5)

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

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

Author: dependabot[bot]

backend/requirements.txt

@@ -58,7 +58,7 @@ tinycss2==1.1.0
 toml==0.10.2
 typed-ast==1.4.2
 typing-extensions==3.7.4.3
-urllib3==1.26.4
+urllib3==1.26.5
 uWSGI==2.0.19.1
 webencodings==0.5.1
 websocket-client==0.58.0