I am trying to run this tutorial notebook, and on PyMC 4.3, the following call returns an error:

```
az.plot_lm(
idata=idata,
y="obs",
x=predictor_scaled,
kind_pp="hdi",
y_kwargs={"color": "C0", "marker": "o", "ms": 4, "alpha": 0.4},
y_hat_fill_kwargs=dict(fill_kwargs={"alpha": 0.8}, color="xkcd:jade"),
axes=ax,
)
```

The error message is `ValueError: x and y must have same first dimension, but have shapes (100,) and (1,)`

.

In contrast, the following minimalist example from arviz does work:

```
import arviz as az
import numpy as np
import xarray as xr
idata = az.load_arviz_data('regression1d')
x = xr.DataArray(np.linspace(0, 1, 100))
idata.posterior["y_model"] = idata.posterior["intercept"] + idata.posterior["slope"]*x
az.plot_lm(idata=idata, y="y", x=x)
```

I tried to inspect the two `idata`

’s manually but couldn’t spot any issue. Does anyone have an idea?