BUG: `make_compute_graph` creates self loop

[williambdean]

I did just catch this bug: It comes from the make_compute_graph which causes a self loop

from pymc.model_graph import ModelGraph

coords = {
    "obs": range(5),
}
with pm.Model(coords=coords) as model:
    data = pt.as_tensor_variable(
        np.ones((5, 3)),
        name="C",
    )
    pm.Deterministic("C", data, dims=("obs", None))

error_compute_graph = ModelGraph(model).make_compute_graph() # defaultdict(set, {"C": {"C"}})
# Visualize error:
pm.model_to_graphviz(model)

Result:

Originally posted by @wd60622 in #7392 (comment)

[moh-dev-stack]

Take