STYLE don't use in-line comments for configuring flake8

[MarcoGorelli]

Check this note from the flake8 docs:

Following the recommended settings for Python’s configparser, Flake8 does not support inline comments for any of the keys. So while this is fine:

[flake8]
per-file-ignores =
# imported but unused
init.py: F401

this is not:

[flake8]
per-file-ignores =
init.py: F401 # imported but unused

However, that's exactly what we do:

pandas/setup.cfg

Lines 71 to 104 in 98e2229

	[flake8]
	max-line-length = 88
	ignore =
	E203, # space before : (needed for how black formats slicing)
	W503, # line break before binary operator
	W504, # line break after binary operator
	E402, # module level import not at top of file
	E731, # do not assign a lambda expression, use a def
	S001, # found modulo formatter (incorrect picks up mod operations)
	B005, # controversial
	B006, # controversial
	B007, # controversial
	B008, # controversial
	B009, # setattr is used to side-step mypy
	B010, # getattr is used to side-step mypy
	B011, # tests use assert False
	B015, # tests use comparisons but not their returned value
	B301 # false positives
	exclude =
	doc/sphinxext/*.py,
	doc/build/*.py,
	doc/temp/*.py,
	.eggs/*.py,
	versioneer.py,
	env # exclude asv benchmark environments from linting
	per-file-ignores =
	# private import across modules
	pandas/tests/*:PDF020
	# pytest.raises without match=
	pandas/tests/extension/*:PDF009
	# os.remove
	doc/make.py:PDF008
	# import from pandas._testing
	pandas/testing.py:PDF014

In each case, the comment should be moved to be on its own line, on the line before the code

Else, we risk accidentally putting something in the comments that'll mess with how flake8 works

[RhnSharma]

I would like to take this one.

[MarcoGorelli]

awesome, PRs welcome