Bump urllib3 from 1.26.2 to 1.26.3

Bumps [urllib3](https://github.com/urllib3/urllib3) from 1.26.2 to 1.26.3.
- [Release notes](https://github.com/urllib3/urllib3/releases)
- [Changelog](https://github.com/urllib3/urllib3/blob/main/CHANGES.rst)
- [Commits](urllib3/urllib3@1.26.2...1.26.3)

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

requirements-dev.txt

@@ -104,7 +104,7 @@ traitlets==5.0.5
 twine==3.2.0
 typed-ast==1.4.1
 typing-extensions==3.7.4.3
-urllib3==1.26.2
+urllib3==1.26.3
 virtualenv==20.2.1
 wcwidth==0.2.5
 webencodings==0.5.1