fix: Raise exception for `probs` with observable

[speller26]

Issue #, if available: #279

Description of changes:

Testing done:

Merge Checklist

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[codecov[bot]]

Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 100.00%. Comparing base (46c674d) to head (f0c92eb). :warning: Report is 19 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #280   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            7         7           
  Lines         1256      1258    +2     
  Branches       179       180    +1     
=========================================
+ Hits          1256      1258    +2     

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