[python linting] enforce E712: Comparison to true should be 'if cond is true:' or 'if cond:'

Summary:
Note that with the RPC results it's worth checking they are exactly
as expected using is operator, but usually we just want to do a
boolean cast.

Depends on D5199

Test Plan:
ninja check-all
arc lint --everything

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D5200