Do not use mismatch in ancestor matching when using infer()

[hyanwong]

Fixes #980

[jeromekelleher]

LGTM. We should update the changelog to note this change in behaviour (technically breaking change)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.17%. Comparing base (0a83c7b) to head (2fdf149).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #981   +/-   ##
=======================================
  Coverage   93.17%   93.17%           
=======================================
  Files          18       18           
  Lines        6370     6370           
  Branches     1086     1086           
=======================================
  Hits         5935     5935           
  Misses        296      296           
  Partials      139      139           

Flag	Coverage Δ
C	93.17% <ø> (ø)
python	95.52% <ø> (ø)

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