MNT add dtype preservation tag to BernoulliRBM (scikit-learn#24318)

Author: svenstehle

sklearn/neural_network/_rbm.py

@@ -447,5 +447,6 @@ def _more_tags(self):
                 "check_methods_sample_order_invariance": (
                     "fails for the score_samples method"
                 ),
-            }
+            },
+            "preserves_dtype": [np.float64, np.float32],
         }