Fixed cost function print when using multi_threads

[pariterre]

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[codecov]

Codecov Report

Merging #399 (1b6db56) into master (2579395) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #399   +/-   ##
=======================================
  Coverage   88.98%   88.98%           
=======================================
  Files          39       39           
  Lines        5953     5954    +1     
=======================================
+ Hits         5297     5298    +1     
  Misses        656      656           

Impacted Files	Coverage Δ
bioptim/limits/penalty_option.py	92.30% <100.00%> (+0.07%)	⬆️
bioptim/optimization/solution.py	85.18% <100.00%> (-0.03%)	⬇️

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