Fix disabled add train button

[achrafmohye]

Closes #8170

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 28.13%. Comparing base (4070d78) to head (c703729).
Report is 3 commits behind head on dev.

Files	Patch %	Lines
...cations/operationalStudies/views/v2/ScenarioV2.tsx	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##                dev    #8172      +/-   ##
============================================
- Coverage     28.14%   28.13%   -0.02%     
+ Complexity     2120     2116       -4     
============================================
  Files          1302     1302              
  Lines        158970   158963       -7     
  Branches       3182     3179       -3     
============================================
- Hits          44740    44720      -20     
- Misses       112321   112334      +13     
  Partials       1909     1909              

Flag	Coverage Δ
core	75.40% <ø> (-0.03%)	⬇️
editoast	70.37% <ø> (-0.04%)	⬇️
front	9.98% <0.00%> (-0.01%)	⬇️
gateway	2.03% <ø> (ø)
railjson_generator	87.49% <ø> (ø)
tests	73.18% <ø> (ø)

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[Uriel-Sautron]

LGTM !! Tested

[flomonster]

LGTM

[SharglutDev]

Lgtm, thank you