Update flake8 requirement from >=3.5.0 to >=7.3.0

Updates the requirements on [flake8](https://github.com/pycqa/flake8) to permit the latest version.
- [Commits](PyCQA/flake8@3.5.0...7.3.0)

---
updated-dependencies:
- dependency-name: flake8
  dependency-version: 7.3.0
  dependency-type: direct:production
...

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

Author: dependabot[bot]

requirements.txt

@@ -8,7 +8,7 @@ pytest>=3.6
 nbval>=0.9.0
 pytest-cov>=2.6.0
 
-flake8>=3.5.0
+flake8>=7.3.0
 
 sphinx<8.2.0
 sphinx_book_theme