Passing multiple --data arguments to `shacl v`

### Version

4.9.0

### Feature

When I run `shacl v --data data1.ttl --data data2.ttl --shapes shapes.ttl` only the last data graph is validated

I expected that all values of `--data` would be merged and validated together

### Are you interested in contributing a solution yourself?

None

Start by tracing how the `shacl v` command handles repeated `--data` arguments, using `data1.ttl`, `data2.ttl`, and `shapes.ttl` as the reproduction inputs. Confirm that both data graphs are merged before validation and that the combined graph is validated against `shapes.ttl`.

Written by the indexing model from the issue text.