Bump flake8-bugbear from 21.3.2 to 21.4.3 (#299)

Bumps [flake8-bugbear](https://github.com/PyCQA/flake8-bugbear) from 21.3.2 to 21.4.3.
- [Release notes](https://github.com/PyCQA/flake8-bugbear/releases)
- [Commits](PyCQA/flake8-bugbear@21.3.2...21.4.3)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements_dev.txt

@@ -1,7 +1,7 @@
 black==20.8b1
 coverage==5.5
 flake8==3.9.0
-flake8-bugbear==21.3.2
+flake8-bugbear==21.4.3
 m2r==0.2.1
 mypy==0.812
 pip