[MRG] Fix warning bug in sinkhorn2

[arincbulgur]

Types of changes

warn argument was not passed downstream sinkhorn_knopp and sinkhorn_log methods and hence it was not possible to suppress warnings appearing inside those methods. It's fixed now.

Motivation and context / Related issue

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.

[rflamary]

Hello @arincbulgur and thank you for the PR.

Could you please update the test_convergence_warning test in test/test_bregman.py that check that the warning is there (and basically also chect that it is not there when warn=Falsein the same tets function)?

[rflamary]

Thanks @arincbulgur , merging now!