Missing import in multinomial_vae.py and standard_vae.py

[miguelgfierro]

Description

VAE algos failing due to missing import

Related Issues

#1504

Checklist:

• I have followed the contribution guidelines and code style for this project.
• I have added tests covering my contributions.
• I have updated the documentation accordingly.
• This PR is being made to staging branch and not to main branch.

[codecov-commenter]

Codecov Report

Merging #1508 (987957e) into staging (3e23511) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@             Coverage Diff             @@
##           staging    #1508      +/-   ##
===========================================
- Coverage    61.96%   61.95%   -0.01%     
===========================================
  Files           84       84              
  Lines         8368     8369       +1     
===========================================
  Hits          5185     5185              
- Misses        3183     3184       +1     

Impacted Files	Coverage Δ
recommenders/models/vae/multinomial_vae.py	0.00% <ø> (ø)
recommenders/models/vae/standard_vae.py	0.00% <0.00%> (ø)

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[miguelgfierro]

merging this since it was approved by the original requester: #1504 (comment)