[LINTER] Enable new autopep8 rules

Summary:
This enables rules that are disabled by default:

E226 - Fix missing whitespace around arithmetic operator.
E241 - Fix extraneous whitespace around keywords.
E242 - Remove extraneous whitespace around operator.

This is a follow-up from this request:
https://reviews.bitcoinabc.org/D4424?id=14076#inline-27270

Test Plan:
Should return no error:

arc lint --everything

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Subscribers: markblundeberg

Differential Revision: https://reviews.bitcoinabc.org/D4755