Fix ignore_index in jaccard index

[SkafteNicki]

What does this PR do?

Fixes #1385

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• Did you make sure to update the docs?
• Did you write any new necessary tests?

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[Borda]

@SkafteNicki is this ready for review? 🐰

[codecov]

Codecov Report

Merging #1386 (da770de) into master (2850524) will decrease coverage by 37%.
The diff coverage is 100%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1386     +/-   ##
========================================
- Coverage      87%     50%    -37%     
========================================
  Files         219     219             
  Lines       11528   11531      +3     
========================================
- Hits        10007    5776   -4231     
- Misses       1521    5755   +4234