Bump flake8 from 5.0.4 to 6.0.0 in /requirements

Bumps [flake8](https://github.com/pycqa/flake8) from 5.0.4 to 6.0.0.
- [Release notes](https://github.com/pycqa/flake8/releases)
- [Commits](PyCQA/flake8@5.0.4...6.0.0)

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

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

requirements/codestyle.txt

@@ -1,9 +1,9 @@
 -r system.txt
 
 # flake8 is required by flake8-mutable
-flake8==5.0.4 \
-    --hash=sha256:6fbe320aad8d6b95cec8b8e47bc933004678dc63095be98528b7bdd2a9f510db \
-    --hash=sha256:7a1cf6b73744f5806ab95e526f6f0d8c01c66d7bbe349562d22dfca20610b248
+flake8==6.0.0 \
+    --hash=sha256:3833794e27ff64ea4e9cf5d410082a8b97ff1a06c16aa3d2027339cd0f1195c7 \
+    --hash=sha256:c61007e76655af75e6785a931f452915b371dc48f56efd765247c8fe68f2b181
 flake8-mutable==1.2.0 \
     --hash=sha256:ee9b77111b867d845177bbc289d87d541445ffcc6029a0c5c65865b42b18c6a6 \
     --hash=sha256:38fd9dadcbcda6550a916197bc40ed76908119dabb37fbcca30873666c31d2d5