Fix variable naming

[Ipuch]

related to #593 i think so.

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This change is 

[codecov]

Codecov Report

Base: 81.54% // Head: 81.54% // No change to project coverage 👍

Coverage data is based on head (ebd4c7d) compared to base (a4b80e6).
Patch coverage: 94.44% of modified lines in pull request are covered.

❗ Current head ebd4c7d differs from pull request most recent head 9e9b6a1. Consider uploading reports for the commit 9e9b6a1 to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #597   +/-   ##
=======================================
  Coverage   81.54%   81.54%           
=======================================
  Files         105      105           
  Lines       11739    11739           
=======================================
  Hits         9572     9572           
  Misses       2167     2167           

Impacted Files	Coverage Δ
bioptim/dynamics/configure_problem.py	90.97% <90.90%> (ø)
bioptim/dynamics/dynamics_functions.py	94.18% <100.00%> (ø)

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[pariterre]

LGTM