Fix cholesky test for quaternionic tridiagonals

[dkarrasch]

Fixes #1414.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.87%. Comparing base (7e647cf) to head (5ed0514).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #1416   +/-   ##
=======================================
  Coverage   93.87%   93.87%           
=======================================
  Files          34       34           
  Lines       15851    15851           
=======================================
  Hits        14880    14880           
  Misses        971      971           

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[dkarrasch]

I think my previous tests were actually flawed. They pass on many examples, but not systematically. You can't trick math. 😅

[ViralBShah]

Thanks for the quick fix!