Wrap callable in union syntax

[cdce8p]

Followup to #20332 (comment)

Wrap the callable with ( ) if it's within a union to reduce ambiguity. This matches the pyright behavior.

def f1() -> int | None: return 1
def f2() -> int: return 1

reveal_type(f1)                     # def () -> builtins.int | None
reveal_type(f2 if int() else None)  # (def () -> builtins.int)) | None

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅

[hauntsaninja]

Nice, thank you!