mypy does not recognize tuple unpacking syntax for TypeVars.

Bug Report

This is really a minor issue, but if you declare multiple TypeVar variables in one line, mypy does not seem to recognize them as type variables. For example,

from typing import TypeVar, Generic
T1, T2 = TypeVar('T1'), TypeVar('T2')

class Container(Generic[T1]):
    class Item(Generic[T2]):
        pass

To Reproduce

1. Declare more than one TypeVars in one line. (See the example code above.)
2. Run mypy check on this script.

Expected Behavior

The T1 and T2 in the example above should be recognized as type variables.
They should pass mypy check.

Actual Behavior

Errors:

$ mypy typevar.py 
typevar.py:5: error: Free type variable expected in Generic[...]
typevar.py:6: error: Free type variable expected in Generic[...]
Found 2 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: 0.910
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.10.0
• Operating system and version: Ubuntu 20.04

提供された Python スニペットと mypy typevar.py コマンドで問題を再現し、その後、Generic[...] を確認する前にタプル代入された TypeVars がどのように認識されるかを追跡します。T1 と T2 の両方が型変数として受け入れられ、例がエラーなしで mypy を通過すれば完了です。