Update lightfm_utils.py

[Ransaka]

LightFm model predict method expect user_ids type of int or np.int32 data type. Made small change on prepare_all_predictions.

Description

Related Issues

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.

[miguelgfierro]

looks good, I'll wait for the test to pass

[codecov-commenter]

Codecov Report

Merging #1624 (b37a577) into staging (d005c1a) will increase coverage by 57.00%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##           staging    #1624       +/-   ##
============================================
+ Coverage     0.00%   57.00%   +57.00%     
============================================
  Files           88       88               
  Lines         8956     8956               
============================================
+ Hits             0     5105     +5105     
- Misses           0     3851     +3851     

Flag	Coverage Δ
nightly	?
pr-gate	57.00% <100.00%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
recommenders/models/lightfm/lightfm_utils.py	62.50% <ø> (+62.50%)	⬆️
recommenders/models/rbm/rbm.py	83.60% <100.00%> (+83.60%)	⬆️
recommenders/datasets/mind.py	0.00% <0.00%> (ø)
recommenders/datasets/movielens.py	69.46% <0.00%> (+69.46%)	⬆️
recommenders/models/sasrec/model.py	26.28% <0.00%> (+26.28%)	⬆️
recommenders/models/sasrec/sampler.py	89.58% <0.00%> (+89.58%)	⬆️
recommenders/datasets/download_utils.py	90.00% <0.00%> (+90.00%)	⬆️
recommenders/models/newsrec/models/npa.py	95.58% <0.00%> (+95.58%)	⬆️
recommenders/models/newsrec/models/naml.py	92.43% <0.00%> (+92.43%)	⬆️
recommenders/models/newsrec/models/nrms.py	91.37% <0.00%> (+91.37%)	⬆️
... and 13 more

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