editoast: add 'label' to towed rolling stock

[woshilapin]

Follow up of #9202. We're missing a long name. I used label.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 39.59%. Comparing base (dffb4b0) to head (e66220e).
Report is 6 commits behind head on dev.

Files with missing lines	Patch %	Lines
editoast/src/models/towed_rolling_stock.rs	0.00%	2 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##                dev    #9465      +/-   ##
============================================
- Coverage     39.63%   39.59%   -0.05%     
  Complexity     2270     2270              
============================================
  Files          1301     1300       -1     
  Lines         99071    99154      +83     
  Branches       3284     3282       -2     
============================================
- Hits          39271    39262       -9     
- Misses        57867    57959      +92     
  Partials       1933     1933              

Flag	Coverage Δ
core	75.07% <ø> (+0.09%)	⬆️
editoast	73.20% <71.42%> (-0.05%)	⬇️
front	10.23% <ø> (ø)
gateway	2.19% <ø> (-0.31%)	⬇️
osrdyne	3.29% <ø> (-0.01%)	⬇️
railjson_generator	87.49% <ø> (ø)
tests	86.71% <ø> (ø)

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[leovalais]

LGTM