Fix example for Object._set documentation

[KoBeWi]

The method is supposed to return true if the property was set (interestingly the C# example is correct).
Though I wonder if the example shouldn't be improved; it's technically incomplete, because a user might not know what to put instead of print.

[akien-mga]

Maybe showing a real example of a fake property that actually does something useful would be good indeed.

[YuriSizov]

If we add a more practical example, prints are probably not needed anymore. Can be kept as code comments instead (i.e. replace prints with # Storing the value in the fake property. or something).

[YuriSizov]

Looks fine. My suggestion was addressed.

[raulsntos]

The C# example looks good to me.

[YuriSizov]

Thanks!

[YuriSizov]

Cherry-picked for 4.1.3.