Fix inference of protocol against overloaded function (#12227)
We used to infer a callable in a protocol against all overload
items. This could result in incorrect results, if only one
of the overload items would actually match the protocol.
Fix the issue by only considering the first matching overload
item.
This seems to help with protocols involving `__getitem__`.
In particular, this fixes regressions related to
`SupportsLenAndGetItem`, which is used for `random.choice`.
