🩹 Fix config file discovery

[s-weigand]

Besides "flake8" being hardcoded in flake8.options.config so is the config file name ".flake8" which needs to be replaces with ".flake8_nb" to prevent a regression where ".flake8_nb is ignored.
The other problem with the discovery of config files was that the config discovery happens in Application.initialize which means that the runtime module replacement needs to happen before this and the config module also needs to be replaced inside of flake8.main.application.

closes #254

[sourcery-ai]

Sourcery Code Quality Report

❌  Merging this PR will decrease code quality in the affected files by 0.25%.

Quality metrics	Before	After	Change
Complexity	4.12 ⭐	3.79 ⭐	-0.33 👍
Method Length	94.05 🙂	98.14 🙂	4.09 👎
Working memory	5.52 ⭐	5.66 ⭐	0.14 👎
Quality	71.10% 🙂	70.85% 🙂	-0.25% 👎

Other metrics	Before	After	Change
Lines	556	595	39

Changed files	Quality Before	Quality After	Quality Change
flake8_nb/flake8_integration/cli.py	69.81% 🙂	69.96% 🙂	0.15% 👍
tests/test__main__.py	73.08% 🙂	71.96% 🙂	-1.12% 👎

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
flake8_nb/flake8_integration/cli.py	Flake8NbApplication.parse_configuration_and_cli	12 🙂	205 ⛔	9 🙂	48.59% 😞	Try splitting into smaller methods
flake8_nb/flake8_integration/cli.py	get_notebooks_from_args	12 🙂	142 😞		53.82% 🙂	Try splitting into smaller methods
flake8_nb/flake8_integration/cli.py	Flake8NbApplication.set_flake8_option	9 🙂	97 🙂	10 😞	60.63% 🙂	Extract out complex expressions
tests/test__main__.py	test_run_main	3 ⭐	189 😞	7 🙂	62.90% 🙂	Try splitting into smaller methods
tests/test__main__.py	test_syscall	2 ⭐	180 😞	7 🙂	64.65% 🙂	Try splitting into smaller methods

Legend and Explanation

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[github-actions]

👈 Launch a binder notebook on branch s-weigand/flake8-nb/fix-config-discovery

[codecov]

Codecov Report

Merging #255 (f0bef52) into main (4bc29af) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##              main      #255   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            5         5           
  Lines          429       431    +2     
  Branches        74        74           
=========================================
+ Hits           429       431    +2     

Impacted Files	Coverage Δ
flake8_nb/flake8_integration/cli.py	100.00% <100.00%> (ø)

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