Add multiple pointers for one test

I want to be able to do something like this:

```python
    @pytest.mark.pointer(target=EnvConfig.get)
    @pytest.mark.pointer(target=EnvConfig.__getitem__)
    def test_get(self):
```

Instead of writing the same test twice.

In the example above the `EnvConfig.__getitem__` would get picked up but not the other one.