42 in "some string" fails at runtime with TypeError but is allowed in typeshed

[ilevkivskyi]

str.__contains__() is annotated as accepting object, but in fact it only accepts strings. Fixing the annotation will require a # type: ignore since this will be an incompatible override.

There is a similar problem with bytes.__contains__(), it only accepts int and bytes.

[ilevkivskyi]

This was discovered in context of python/mypy#6674