[numpy] Fix users of NumPy APIs that are removed in NumPy 2.0.

This change migrates users of APIs removed in NumPy 2.0 to their recommended replacements (https://numpy.org/devdocs/numpy_2_0_migration_guide.html).

PiperOrigin-RevId: 657176440

edward2/tensorflow/layers/heteroscedastic_test.py

@@ -633,7 +633,7 @@ def train_step(inputs, labels, model):
 
     if kwargs.get('tune_temperature'):
       contains_temperature = False
-      pre_sigmoid_temperature = np.NaN
+      pre_sigmoid_temperature = np.nan
       for w in classifier.trainable_weights:
         if 'pre_sigmoid_temperature' in w.name:
           contains_temperature = True