Wrong typechecking with Literal['a','b','c'] for params unpacked from **{"arg":"a"}

### Describe the Bug

```python
def fun(arg:Literal['a','b','c']):
pass

params={'arg':'a'}
fun(**params) # Argument `str` is not assignable to parameter `arg` with type `Literal['a', 'b', 'b']` in function `fun`Pyrefly[bad-argument-type](https://pyrefly.org/en/docs/error-kinds/#bad-argument-type)
```

### Sandbox Link

_No response_

### (Only applicable for extension issues) IDE Information

pyrefly version 1.2.0

Start with the Python reproduction in the issue and trace Pyrefly's handling of arguments unpacked from **params during Literal inference. Done when the shown call is accepted without a bad-argument-type diagnostic and the behavior is covered by a regression test.

Written by the indexing model from the issue text.