Bump flake8 from 3.7.9 to 7.1.1 in /requirements

Bumps [flake8](https://github.com/pycqa/flake8) from 3.7.9 to 7.1.1.
- [Commits](PyCQA/flake8@3.7.9...7.1.1)

---
updated-dependencies:
- dependency-name: flake8
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>

requirements/tests.txt

@@ -1,5 +1,5 @@
 coveralls==1.8.2
-flake8==3.7.9
+flake8==7.1.1
 pytest==5.2.4
 pytest-cov==2.8.1
 cov-core==1.15.0