Upcasting causes incompatible types in assignment with TypedDict

[sterliakov]

Bug Report

Type checking the code below causes mypy errors. In my opinion, everything assignable to type T should be still assignable to type T | something.

To Reproduce

Playground with the following code:

from typing import TypedDict


class AngleDict(TypedDict):
    yaw: float
    pitch: float
    roll: float
    

angles: dict[str, None] = {"yaw": None, "pitch": None, "roll": None}
angles2: AngleDict | dict[str, None] = {"yaw": None, "pitch": None, "roll": None}

Expected Behavior

No errors.

Actual Behavior

main.py:11: error: Incompatible types (expression has type "None", TypedDict item "yaw" has type "float")  [typeddict-item]
main.py:11: error: Incompatible types (expression has type "None", TypedDict item "pitch" has type "float")  [typeddict-item]
main.py:11: error: Incompatible types (expression has type "None", TypedDict item "roll" has type "float")  [typeddict-item]
Found 3 errors in 1 file (checked 1 source file)

Your Environment

• Mypy version used: master and 1.1.1
• Mypy command-line flags: nope
• Mypy configuration options from mypy.ini (and other config files): nope
• Python version used: 3.10, 3.11