Generic with ParamSpec and Concatenate substitutions behave incorrectly

[Daraan]

The following code displays some incorrect behavior, but different parts do not work in certain ranges of 3.8-3.11.3

• 3.8 & 3.9 substitution of Concatenate
• 3.10 does not correctly collect type parameters
• < 3.11.3 wrong substitution behavior; type parameter not removed

from typing import Generic, TypeVar
from typing_extensions import ParamSpec, Concatenate
P = ParamSpec('P')
T = TypeVar("T")

class CLS(Generic[P]): ...

Y = CLS[T] # or with a ParamSpec
# 3.10
Y[str]  # raises TypeError is not a generic class

# 3.8 & 3.9
G9 = CLS[Concatenate[T, P]]
H9 = G9[int, [T]] # should be ok; but TypeError
H9[str]  # should also work

# 3.11.0
G8 = CLS[Concatenate[T, ...]]
H1 = G8[int]
H1[str]  # for python 3.11.0-3 this still has a parameter and does not raise a TypeError

This is a variant of #126 but with generics which require different fixes. There are multiple flavors of this issue depending on the version parameters are not recognized or not substituted correctly.

For a more comprehensive list check the skipped tests of #491 here

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It's possible that some substitutions with Concatenate worked prior to #479 and caused a regression here, but I am not yet certain.

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Fixes come with

• Fix Concatenate and Generic with ParamSpec substitution #489