🐛 Force return on load for old style datasets (#592)

[Galileo-Galilei]

Description

Close #592

Development notes

add a return statement on MLflowArtifactDataset._load for old style dataset

Checklist

• Read the contributing guidelines
• Open this PR as a 'Draft Pull Request' if it is work-in-progress
• Update the documentation to reflect the code changes
• Add a description of this change and add your name to the list of supporting contributions in the CHANGELOG.md file. Please respect Keep a Changelog guidelines.
• Add tests to cover your changes

Notice

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[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 100.00%. Comparing base (3351137) to head (5b298ed).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #593   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           29        29           
  Lines         1030      1032    +2     
=========================================
+ Hits          1030      1032    +2     

Flag	Coverage Δ
	100.00% <ø> (?)

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