Use flake518 instead of pflake8

[astariul]

🔍️ Description

flake518 seems to be a more up-to-date alternative to pflake8. Let's use that.

✅ How this was tested ?

pre commit pass.

🌱 Checklist

• Perform self-review of my own code
• Comment the code, particularly in hard-to-understand areas
• Update the documentation accordingly to the new code
• Lint / format the code
• Update existing tests / Add new tests
• Tests are passing locally