fix Concrete type not assignable to gradual type when TypeVarTuple is involved #4609

[asukaminato0721]

Summary

Fixes #4609

removes an extra tuple wrapper around forwarded *Ts arguments before checking assignability.

Test Plan

add test

[meta-codesync]

This pull request has been imported. If you are a Meta employee, you can view this in D119092691. (Because this pull request was imported automatically, there will not be any future comments.)

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

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SUMMARY
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Total: +0 new errors, -3 fixed errors
By preset: +0/-3 (default), +0/-3 (strict)

Projects with changes (2):
  core: +0 -2
  trio: +0 -1
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FULL DIFF DETAILS
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core (https://github.com/home-assistant/core)
- ERROR homeassistant/components/rfxtrx/entity.py:126:47-81: Unpacked argument `tuple[Unknown, *_Ts]` is not assignable to parameter `*args` with type `tuple[Unknown, *_Ts]` in function `homeassistant.core.HomeAssistant.async_add_executor_job` [bad-argument-type]
- ERROR homeassistant/helpers/dispatcher.py:133:35-88: Unpacked argument `tuple[HomeAssistant, SignalType[*_Ts], *_Ts]` is not assignable to parameter `*args` with type `tuple[HomeAssistant, SignalType[*_Ts] | str, *_Ts]` in function `asyncio.events.AbstractEventLoop.call_soon_threadsafe` [bad-argument-type]

trio (https://github.com/python-trio/trio)
- ERROR src/trio/_dtls.py:1328:35-50: Unpacked argument `tuple[DTLSChannel, *PosArgsT]` is not assignable to varargs type `tuple[DTLSChannel, *PosArgsT]` [bad-argument-type]