Extend ignore list in flake8 config

flake8 disables a number of checks by default, e.g. W503 [1] and W504
[2], which are conflicting checks and are both not violations of the
PEP8 standard. In the flake8 config, the `ignore` key overrides the
default ignore list, leading to these issues being raised in CI. The
`extend-ignore` key extends the default ignore list instead, allowing
these issues to correctly remain suppressed.

[1]: https://www.flake8rules.com/rules/W503.html
[2]: https://www.flake8rules.com/rules/W504.html

Author: snprajwal

.github/workflows/configs/.flake8

@@ -1,6 +1,6 @@
 [flake8]
 
-ignore =
+extend-ignore =
     # These are needed to make our license headers pass the linting
     E265,
     E266,