front: double scrollbar when switching to package sorting

[Maymanaf]

What happened?

scroll.mp4

What did you expect to happen?

A single scrollbar with the correct scroll thumb size

How can we reproduce it (as minimally and precisely as possible)?

1. Go to a scenario with a large timetable
2. Sort by package

On which environments the bug occurs?

Recette (SNCF)

On which browser the bug occurs?

Firefox, Google Chrome

OSRD version (top right corner Account button > Informations)

770a507