accept_rate_iter should always be an array

Author: jessegrabowski

pymc/step_methods/metropolis.py

@@ -308,13 +308,12 @@ def astep(self, q0: RaveledVars) -> tuple[RaveledVars, StatsType]:
         else:
             accept_rate = self.delta_logp(q, q0d)
             q, accepted = metrop_select(accept_rate, q, q0d, rng=self.rng)
-            self.accept_rate_iter = accept_rate
+            self.accept_rate_iter[:] = accept_rate
             self.accepted_iter[0] = accepted
             self.accepted_sum += accepted
 
         self.steps_until_tune -= 1
 
-        self.accept_rate_iter = np.atleast_1d(self.accept_rate_iter)
         log_N = np.log(self.accept_rate_iter.shape[0])
 
         stats = {