Add rubygem_id foreign key constraint to linksets table.

[simi]

There is 1 old linklist breaking this foreign key.

@martinemde @segiddins would you prefer to make the deletion in migration or is it ok to delete manually to keep prod DB inconsistency details out of migrations?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.07%. Comparing base (b896042) to head (02018b6).
Report is 5 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4571   +/-   ##
=======================================
  Coverage   97.07%   97.07%           
=======================================
  Files         390      390           
  Lines        8181     8181           
=======================================
  Hits         7942     7942           
  Misses        239      239           

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[martinemde]

If you fix it manually, other environments might need to be manually cleaned as well, but that seems fine as it allows local envs to clean up their own way. I'm ok with deploying this as is.

[segiddins]

Deleting manually sounds right to me