Fix computing duals

[manuelma]

Checklist before merging

• Documentation is up-to-date
• Unit tests have been added/updated accordingly
• Code has been formatted according to SpineOpt's style
• Unit tests pass

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.27%. Comparing base (9a6b791) to head (79ea9f0).

Files with missing lines	Patch %	Lines
src/run_spineopt_basic.jl	85.71%	1 Missing ⚠️

Additional details and impacted files

@@                 Coverage Diff                  @@
##           v0.7.2.x-release    #1091      +/-   ##
====================================================
+ Coverage             86.14%   86.27%   +0.13%     
====================================================
  Files                   141      141              
  Lines                  3731     3724       -7     
====================================================
- Hits                   3214     3213       -1     
+ Misses                  517      511       -6     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.