[ITensors] Fix non-QN eigen with auto-fermion enabled

[mtfishman]

@b-kloss I think you were hitting this in ITensorNetworks.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.59%. Comparing base (e8197ce) to head (106a410).
Report is 2 commits behind head on main.

❗ Current head 106a410 differs from pull request most recent head de7be59. Consider uploading reports for the commit de7be59 to get more accurate results

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Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1380   +/-   ##
=======================================
  Coverage   79.59%   79.59%           
=======================================
  Files         114      114           
  Lines        9032     9032           
=======================================
  Hits         7189     7189           
  Misses       1843     1843           

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