Fix: Update SparseCategoricalCrossentropy example

[sonali-kumari1]

Update SparseCategoricalCrossentropy example to resolve ValueError: Structures don't have the same nested structure. Gist

Fixes : #21426

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.72%. Comparing base (3d6022a) to head (4242b42).
Report is 3 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #21427   +/-   ##
=======================================
  Coverage   82.72%   82.72%           
=======================================
  Files         565      565           
  Lines       55222    55222           
  Branches     8609     8609           
=======================================
  Hits        45683    45683           
  Misses       7428     7428           
  Partials     2111     2111           

Flag	Coverage Δ
keras	82.53% <ø> (ø)
keras-jax	63.33% <ø> (ø)
keras-numpy	58.53% <ø> (+<0.01%)	⬆️
keras-openvino	33.79% <ø> (ø)
keras-tensorflow	63.74% <ø> (ø)
keras-torch	63.37% <ø> (ø)

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