Bump pyflakes from 2.3.1 to 2.4.0

Bumps [pyflakes](https://github.com/PyCQA/pyflakes) from 2.3.1 to 2.4.0.
- [Release notes](https://github.com/PyCQA/pyflakes/releases)
- [Changelog](https://github.com/PyCQA/pyflakes/blob/master/NEWS.rst)
- [Commits](PyCQA/pyflakes@2.3.1...2.4.0)

---
updated-dependencies:
- dependency-name: pyflakes
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

requirements-tests.txt

@@ -2,4 +2,4 @@
 pytest==6.2.5
 pytest-cov==3.0.0
 flake8==4.0.0
-pyflakes==2.3.1
+pyflakes==2.4.0