Fix recursive use of Concatenate when mixing modules

[Daraan]

Fixes that this code sample throws an error for 3.10:

P = ParamSpec("P")
typing_extensions.Concatenate[int, P][typing.Concatenate[int, P]]

TypeError: The last parameter to Concatenate should be a ParamSpec variable or ellipsis.

[JelleZijlstra]

Thanks, could you add a changelog entry? Something like "Fix errors on Python 3.10 when typing.Concatenate and typing_extensions.Concatenate are used together."