NBMsgPack012: [KnownSubType] type must be unique

@Nerdbank.MessagePack.KnownSubTypeAttribute should specify a type that is unique within the scope of the type it is applied to.

Learn more about subtype unions.

Example violations

[KnownSubType<DerivedType>(1)]
[KnownSubType<DerivedType>(2)] // assigned second alias to a subtype
class BaseType
{
}

class DerivedType : BaseType
{
}

Resolution

Remove the extra alias or assign it to a different type.

[KnownSubType<DerivedType>(1)]
class BaseType
{
}

class DerivedType : BaseType
{
}