Update Arviz conversion for new missing values approach

Author: brandonwillard

pymc3/backends/arviz.py

@@ -19,6 +19,7 @@
 
 from aesara.graph.basic import Constant
 from aesara.tensor.sharedvar import SharedVariable
+from aesara.tensor.subtensor import AdvancedIncSubtensor
 from arviz import InferenceData, concat, rcParams
 from arviz.data.base import CoordSpec, DimSpec
 from arviz.data.base import dict_to_dataset as _dict_to_dataset
@@ -275,9 +276,10 @@ def log_likelihood_vals_point(self, point, var, log_like_fun):
         # variables some other way
         point = {i.name: point[i.name] for i in log_like_fun.f.maker.inputs if i.name in point}
         log_like_val = np.atleast_1d(log_like_fun(point))
-        if var.tag.missing_values:
+
+        if isinstance(var.owner.op, AdvancedIncSubtensor):
             try:
-                obs_data = extract_obs_data(var)
+                obs_data = extract_obs_data(var.tag.observations)
             except TypeError:
                 warnings.warn(f"Could not extract data from symbolic observation {var}")