Pm.set_data in 4.2.0

Questions v5
3

This is what I get with 4.2:

import pymc as pm

with pm.Model() as model:
    y = pm.MutableData('y', [1., 2., 3.])
    beta = pm.Normal('beta', 0, 1)
    obs = pm.Normal('obs', beta, 1, observed=y)
    idata = pm.sample(1000, tune=1000)
    
with model:
    pm.set_data({'y': [1,2,3,4]})
    y_test = pm.sample_posterior_predictive(idata)

y_test.posterior_predictive['obs'].mean(('chain', 'draw'))

#<xarray.DataArray 'obs' (obs_dim_0: 4)>
#array([1.5213813 , 1.50321493, 1.51028904, 1.52245995])
#Coordinates:
#  * obs_dim_0  (obs_dim_0) int64 0 1 2 3