[v1.4.x] Backport disabled flaky test_softmin (#13758)

[perdasilva]

Description

Backports disabling of flaky test_softmin.
Original PR: #13758
GitHub Issue: #13600

Recent failure: http://jenkins.mxnet-ci.amazon-ml.com/blue/organizations/jenkins/mxnet-validation%2Fwindows-gpu/detail/v1.4.x/56/pipeline/

Checklist

Essentials

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [MXNET-$JIRA_ID], where $JIRA_ID refers to the relevant JIRA issue created (except PRs with tiny changes)
• Changes are complete (i.e. I finished coding on this PR)
• All changes have test coverage:
• Unit tests are added for small changes to verify correctness (e.g. adding a new operator)
• Nightly tests are added for complicated/long-running ones (e.g. changing distributed kvstore)
• Build tests will be added for build configuration changes (e.g. adding a new build option with NCCL)
• Code is well-documented:
• For user-facing API changes, API doc string has been updated.
• For new C++ functions in header files, their functionalities and arguments are documented.
• For new examples, README.md is added to explain the what the example does, the source of the dataset, expected performance on test set and reference to the original paper if applicable
• Check the API doc at http://mxnet-ci-doc.s3-accelerate.dualstack.amazonaws.com/PR-$PR_ID/$BUILD_ID/index.html
• To the my best knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change

[karan6181]

@mxnet-label-bot add [Test, Python, pr-awaiting-review]

[piyushghai]

@marcoabreu Can you review this PR ?

[vandanavk]

Is this PR still required?

[perdasilva]

I have no idea

[roywei]

If we are going to keep 1.4.x nightly CI running, and this fix the failure, we should merge it.

[karan6181]

@perdasilva @roywei steps for merging this PR?

[piyushghai]

@perdasilva What's the path forward for this PR ?

[perdasilva]

I'll close it for now. It's been open for months with no action. If it looks like it is needed again, I can re-open.