Update auto_encoder.py

[Gradwanderer]

Tensorflow keras has changed names to MeanSquaredError. Please accept for the next users.
Could not find any issues on that task. If not accepted, please add a info on the TF version number.
I am using TF 2.15.0

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Updated AutoEncoder

[Gradwanderer]

I have seen the l2 import had to be changed also to L2 (line 24 + 29...)

[yzhao062]

Hi there, the auto tests failed :) feel free to fix them first. thx