Fix return types

[erick-xanadu]

Context: Callbacks was incorrectly returning a list when it should return scalar values.

Description of the Change: Does not modify the shape of the return type pytrees.

Benefits: Fixes issue seen

Possible Drawbacks: None

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.15%. Comparing base (539ff43) to head (6046d83).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #686      +/-   ##
==========================================
- Coverage   99.15%   99.15%   -0.01%     
==========================================
  Files          64       64              
  Lines        9259     9258       -1     
  Branches      719      718       -1     
==========================================
- Hits         9181     9180       -1     
  Misses         51       51              
  Partials       27       27              

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[isaacdevlugt]

Looks good to me! Thanks @erick-xanadu 👍