Fix numpy deprecation warning when running tests in test_metropolis.py

Author: asifzubair

pymc/step_methods/metropolis.py

@@ -1214,7 +1214,7 @@ def astep(self, q0: RaveledVars) -> tuple[RaveledVars, StatsType]:
 
         stats = {
             "tune": self.tune,
-            "scaling": self.scaling,
+            "scaling": np.mean(self.scaling),
             "lambda": self.lamb,
             "accept": np.exp(accept),
             "accepted": accepted,