Update flake8 requirement from <4.0,>=3.9 to >=3.9,<8.0

Updates the requirements on [flake8](https://github.com/pycqa/flake8) to permit the latest version.
- [Commits](PyCQA/flake8@3.9.0...7.1.1)

---
updated-dependencies:
- dependency-name: flake8
  dependency-type: direct:development
...

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

setup.py

@@ -38,7 +38,7 @@
     extras_require = {
         "dev": [
             "autopep8",
-            "flake8>=3.9,<4.0",
+            "flake8>=3.9,<8.0",
             "flake8-import-order",
             "flake8-print",
             "pycodestyle >=2.6.0",