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

Reproduce the issue with the provided Python snippet and the mypy typevar.py command, then trace how tuple-assigned TypeVars are recognized before checking Generic[...]. Done means both T1 and T2 are accepted as type variables and the example passes mypy without errors.