Type is lost after merge with `Union[Any, None]`

Bug Report

from typing import Any

def func(d: dict[int, Any]) -> None:
    x: int | None
    x = d.get(1)
    reveal_type(x)  # typing is lost -> Union[Any, None]

d.get get's correctly inferred as Any | None. However, merging the existing type int | None with Any | None results in Any | None. I.e. mypy looses the original type information. That is unexpected.

Comparing it to a type merge with just Any:

def f(a: Any) -> None:
    x: int | None
    x = a
    reveal_type(x)  # int | None

In this case x retains the type information, as expected.

--
Another example which doesn't rely on dict.get

def g(a: Any | None) -> None:
    x: int | None
    x = a
    reveal_type(x)  # typing is lost -> Union[Any, None]

Expected Behavior

Mypy should retain the original type information even after merging it with Any | None.

Your Environment

• Mypy version used: 0.971

Start with the three reproducer functions in the issue and run them through mypy with reveal_type to confirm the current behavior. Trace the type-merging and assignment logic for an existing int | None value combined with Any | None. Done means the inferred type remains int | None in all shown examples, with regression coverage for these cases.