[red-knot] Fix disambiguate display for union types (#16907)
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## Summary
When callables are displayed in unions, like:
```py
from typing import Callable
def foo(x: Callable[[], int] | None):
# red-knot: Revealed type is `() -> int | None` [revealed-type]
reveal_type(x)
```
This leaves the type rather ambiguous, to fix this we can add
parenthesis to callable type in union
Fixes #16893
## Test Plan
Update callable annotations tests
---------
Co-authored-by: Micha Reiser <micha@reiser.io>
