List should be treated as invalid unpacking targets

[sobolevn]

Rule request

Thesis

Currently, this code passes our linter:

[first, second] = some()

But, it is wrong. We need to force:

first, second = some()

So, we need to disallow ast.List as an unpacking target.

Reasoning

There's an already a working way of doing unpacking assignment: tuples.
We don't need one more way to do it.

I would say this is a consistency rule.

[skarzi]

Can I prepare PR for this issue?

[sobolevn]

@skarzi sure! Thanks a lot!