Issue 13323 - UDA applied to import statement causes compilation to fail without error

https://issues.dlang.org/show_bug.cgi?id=13323
Good catch. Other `AttributeDeclaration`s `newSope` use `Scope::copy()`, but `UserAttributeDeclaration::newScope` uses `Scope::push()` and it resets `sc->scopesym` to `NULL`.

I updated the fix based on the findings.