Type mismatch error with overlapping enums

Bug Report

Enum is casted to literal when asserting its value, even when it is declared as attr of class that can be mutated after assertion

To Reproduce

from enum import Enum


class MyEnum(Enum):
    A = 1
    B = 2


class A:
    def __init__(self, enum: MyEnum):
        self.enum = enum

    def change(self) -> None:
        self.enum = MyEnum.B

if __name__ == "__main__":
    a = A(MyEnum.A)
    assert a.enum == MyEnum.A
    a.change()
    assert a.enum == MyEnum.B  

Expected Behavior

No error

Actual Behavior

Non-overlapping equality check (left operand type: "Literal[MyEnum.A]", right operand type: "Literal[MyEnum.B]")

Your Environment

• Mypy version used: current master
• Mypy command-line flags: --strict
• Python version used: 3.10

Start by running the provided example with mypy --strict on Python 3.10 and inspect how enum equality assertions narrow attributes that can be mutated. Trace the handling of attribute narrowing and enum literals, then add coverage for this reproduction. Done means the example produces no erroneous non-overlapping equality error.