Build(deps): bump urllib3 from 1.25.11 to 2.6.3 in /backend

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.25.11 to 2.6.3.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.25.11...2.6.3)

---
updated-dependencies:
- dependency-name: urllib3
  dependency-version: 2.6.3
  dependency-type: direct:production
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -45,7 +45,7 @@ requests==2.32.0
 six==1.13.0
 sqlparse==0.5.0
 typed-ast
-urllib3==1.25.11
+urllib3==2.6.3
 vine==1.3.0
 virtualenv==16.0.0
 wrapt==1.11.2