[WIP] Fix matrix feature shape in entropic FGW barycenters

[cedricvincentcuaz]

Types of changes

Motivation and context / Related issue

Address Issue #574

How has this been tested (if it applies)

PR checklist

• I have read the CONTRIBUTING document.
• The documentation is up-to-date with the changes I made (check build artifacts).
• All tests passed, and additional code has been covered with new tests.
• I have added the PR and Issue fix to the RELEASES.md file.

[codecov]

Codecov Report

Merging #575 (cf870c8) into master (fcd8f05) will increase coverage by 0.02%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #575      +/-   ##
==========================================
+ Coverage   96.52%   96.54%   +0.02%     
==========================================
  Files          74       74              
  Lines       14859    14870      +11     
==========================================
+ Hits        14342    14356      +14     
+ Misses        517      514       -3