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

All Submissions Basics:

• [x] Have you followed the guidelines in our Contributing document?
• [x] Have you checked to ensure there aren't other open Pull Requests for the same update/change?
• [x] Have you checked all Issues to tie the PR to a specific one?

All Submissions Cores:

• [x] Have you added an explanation of what your changes do and why you'd like us to include them?
• [x] Have you successfully ran tests with your changes locally?

New Model Submissions:

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