false positive: "Overloaded function signatures ... overlap with incompatible return types"

Bug Report

Code of a certain form causes a false positive error:

error: Overloaded function signatures 1 and 2 overlap with incompatible return types  [misc]

To Reproduce

Gist: mypy-play.net

from typing import (
        Literal,
        overload,
        Sequence,
        TypeVar,
        Union,
        )

T1 = TypeVar('T1')
T2 = TypeVar('T2')

@overload
def func(a1: Literal[True], a2: T1) -> Union[T1, Sequence[T2]]: ...
    # error: Overloaded function signatures 1 and 2 overlap with incompatible return types  [misc]

@overload
def func(a1: bool, a2: T1) -> Union[T1, Sequence[T2], T2]: ...

def func(  # type: ignore[empty-body]
        a1: bool, a2: T1) -> Union[T1, Sequence[T2], T2]:
    ...

Expected Behavior

There should be no errors.

• the second signature's arguments are clearly broader than the first's (bool vs. Literal[True])
• the second signature's return type is clearly broader than the first's (Union[...] vs. Union[..., T2])

Actual Behavior

An error is issued:

error: Overloaded function signatures 1 and 2 overlap with incompatible return types  [misc]

Additional notes

This example is fairly minimal:

• removing the a2 argument from all three declarations causes the problem to disappear
• removing the Sequence[T2] clause from the return Union of all three declarations causes the problem to disappear

Your Environment

• Mypy version used: 0.910, 1.8.0
• Mypy command-line flags: (none)
• Mypy configuration options from mypy.ini (and other config files): (none)
• Python version used: 3.8, 3.12

Start by running the linked mypy-play reproducer and narrowing it using the minimal variants described in the issue. No source file or test entry point is identified; done means the example and its stated variants no longer produce the false-positive overload error, with regression coverage added in the appropriate mypy test location.