Fix issue with PEP 585 and 604 syntax

[cdce8p]

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Description

Followup to #4059 and #4075. Fixes multiple smaller issues that occurred while testing.

Nested PEP 585 syntax
This MR fixes a false-positive issue where the new syntax was used inside another type (eg. Union, Dict, ...).

# Python 3.7 / 3.8
from __future__ import annotations
from typing import Dict
var4: Dict[str, list[int]]  # `list` was falsely marked with -> unsubscriptable-object
var7: list[list[int]]       # inner `list` -> unsubscriptable-object

Nested PEP 604 syntax
Fix false-positive issue with unsupported-binary-operation

# Python 3.7 - 3.9
from __future__ import annotations
import typing
var1: typing.Dict[str, int | None]

Improve recognition of invalid PEP 604 syntax
The following will now be correctly marked with unsupported-binary-operation (the future import is missing).

# Python 3.7 - 3.9
var2: int | str | None

Type of Changes

	Type
✓	🐛 Bug fix
✓	✨ New feature
	🔨 Refactoring
	📜 Docs

[coveralls]

Coverage increased (+0.01%) to 90.594% when pulling f183f07 on cdce8p:fix-typing into e48946f on PyCQA:master.

[cdce8p]

cc: @Pierre-Sassoulas