[ty] Ignore `_generate_next_value_` with custom construction hooks (#25210)
## Summary
One oversight in my changes to
https://github.com/astral-sh/ruff/pull/25196: if a custom `__new__` is
defined, we should treat the alias value as `Any`, rather than relying
on `_generate_next_value_`. This matches Pyright, for example.
E.g., given:
```python
class E(Enum):
@staticmethod
def _generate_next_value_(...) -> Literal["x"]:
return "x"
def __new__(cls, value: str):
obj = object.__new__(cls)
obj._value_ = object()
return obj
A = auto()
B = auto()
```
Prior to this change, we treated `B` as an alias of `A`; but if
`__new__` is defined, we don't attempt to detect the alias.
ruff
b81d55ed - [ty] Ignore `_generate_next_value_` with custom construction hooks (#25210)
