Revert "Apply ruff/flake8-comprehensions rule C420 (#13284)"

[ichard26]

I forgot about the fact we can ignore specific rules in advance.

I'm gonna leave this PR open for a few days for what I assume are obvious reasons. There's really no point in making our code less readable over this.

[notatallshaw]

FWIW, I find dict.fromkeys more readable, because I am familiar with the method, and it immediately tells me the value is a constant, whereas for a dictionary comprehension I have to parse the comprehension and determine whether the value is scoped within the comprehension or outside it.

But I do see for those not familiar with the method, dictionary comprehensions are far more common, this requires an extra look up as to what the method does.

And this is so minor, I am neither for or against it.