Updated random_grayscale.py compute_output_spec (#21312)

* Update nn.py

* Update nn.py

* Update nn.py

* Update nn.py

* Update nn.py

Corrected indentation in doc string

* Update nn.py

* Update random_grayscale.py

Fixed issue with passing a single image without batch dimension.

* Update keras/src/layers/preprocessing/image_preprocessing/random_grayscale.py

Co-authored-by: Jyotinder Singh <33001894+JyotinderSingh@users.noreply.github.com>

* Update random_grayscale_test.py

Test case for unbatched inputs

* code reformat

* Update random_grayscale_test.py

Testcase for checking both unbatched and batched single image inputs.

* changed compute_output_spec

There was a bug, and it was causing cycle in graph.

---------

Co-authored-by: Jyotinder Singh <33001894+JyotinderSingh@users.noreply.github.com>

Author: pctablet505

keras/src/layers/preprocessing/image_preprocessing/random_grayscale.py

@@ -1,4 +1,5 @@
 from keras.src import backend
+from keras.src import tree
 from keras.src.api_export import keras_export
 from keras.src.layers.preprocessing.image_preprocessing.base_image_preprocessing_layer import (  # noqa: E501
     BaseImagePreprocessingLayer,
@@ -96,7 +97,12 @@ def compute_output_shape(self, input_shape):
         return input_shape
 
     def compute_output_spec(self, inputs, **kwargs):
-        return inputs
+        return tree.map_structure(
+            lambda x: backend.KerasTensor(
+                x.shape, dtype=x.dtype, sparse=x.sparse
+            ),
+            inputs,
+        )
 
     def transform_bounding_boxes(self, bounding_boxes, **kwargs):
         return bounding_boxes