front: display correct ch code after linked train selection

[SarahBellaha]

Closes #10033

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Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

Project coverage is 81.43%. Comparing base (b09fc36) to head (a465be7).
Report is 26 commits behind head on dev.

Files with missing lines	Patch %	Lines
front/src/reducers/osrdconf/stdcmConf/index.ts	0.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##              dev   #10235      +/-   ##
==========================================
- Coverage   81.44%   81.43%   -0.02%     
==========================================
  Files        1058     1058              
  Lines      104282   104283       +1     
  Branches      722      722              
==========================================
- Hits        84936    84925      -11     
- Misses      19305    19317      +12     
  Partials       41       41              

Flag	Coverage Δ
editoast	73.57% <ø> (-0.05%)	⬇️
front	89.18% <88.88%> (+<0.01%)	⬆️
gateway	2.18% <ø> (ø)
osrdyne	3.28% <ø> (ø)
railjson_generator	87.50% <ø> (ø)
tests	87.05% <ø> (ø)

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[Uriel-Sautron]

LGTM, tested !!!

[kmer2016]

LGTM !