Alias to enum member is treated as separate member

This comes from a recently-filed mypy issue: https://github.com/python/mypy/issues/16830.

```python
from enum import Enum

class TrafficLight(Enum):
    RED = 1
    GREEN = 2
    YELLOW = 3

    AMBER = YELLOW  # Alias for YELLOW

reveal_type(TrafficLight.AMBER)  # Should be Literal[TrafficLight.YELLOW]
```