Bump sphinx from 3.4.2 to 3.4.3

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.4.2 to 3.4.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.4.2...v3.4.3)

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

Author: dependabot-preview[bot]

poetry.lock

@@ -28,7 +28,7 @@ black = {version = "^20.8b1",allow-prereleases = true}
 pytest-cov = "^2.11.0"
 jsonschema = "^3.2.0"
 pylint = "^2.6.0"
-sphinx = "^3.4.2"
+sphinx = "^3.4.3"
 sphinx-autoapi = "^1.4.0"
 sphinx-rtd-theme = "^0.5.1"
 mypy = "^0.790"