Overriding Base.getproperty(vds::Vector{DataStore}, s::Symbol) conflicts `A.ref` usage in julia

This code fails in newer versions of Julia:

```
fill(GraphNeuralNetworks.DataStore(), 3)
```

The implementation of `fill` will ultimately use `A.ref`, where A is a `Vector{DataStore}`.
However, `A.ref` is overridden by this package, and will be interpreted as accessing GNN data.

This overload should check this condition (s===:ref) and use `getfield(vds, :ref)`.
