tests: update fuzzer

[eckter]

There were a couple small elements that weren't up to date with some api changes:

• id -> timetable_id
• None isn't a valid margin option anymore

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 60.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 36.95%. Comparing base (512fe9a) to head (77e35f0).
Report is 4 commits behind head on dev.

Files with missing lines	Patch %	Lines
tests/fuzzer/fuzzer.py	60.00%	2 Missing ⚠️

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Additional details and impacted files

@@             Coverage Diff              @@
##                dev    #8896      +/-   ##
============================================
- Coverage     36.96%   36.95%   -0.02%     
  Complexity     2211     2211              
============================================
  Files          1256     1256              
  Lines        114423   114421       -2     
  Branches       3182     3182              
============================================
- Hits          42298    42280      -18     
- Misses        70234    70250      +16     
  Partials       1891     1891              

Flag	Coverage Δ
core	74.84% <ø> (ø)
editoast	72.40% <ø> (-0.07%)	⬇️
front	14.90% <ø> (ø)
gateway	2.20% <ø> (ø)
osrdyne	2.60% <ø> (ø)
railjson_generator	87.49% <ø> (ø)
tests	86.46% <60.00%> (+0.09%)	⬆️

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[shenriotpro]

Thanks