bicycles do not sink when on tow cable

# Describe the bug

Attaching bicycle type vehicles to floating vehicles lets the player tow the bicycle over water without it sinking.

# Steps To Reproduce

go to a river
spawn an amphibious truck
drive the truck so that all of its tiles are in water
spawn a bicycle
attach the vehicles together starting with the truck
drive the truck across the water
the bicycle will follow you and not sink even if it completely on deep water
drag the bicycle back onto shallow water
detach bicycle from the truck
bicycle will still work normally
repeat the process but stop the truck with the bicycle in deep water
get out of the truck and swim to the bicycle
you can stand on the bicycle like a platform as long as you do not step on the seat

# Expected behavior
Towing a bicycle over deep water should cause it to sink like other vehicles.

# Screenshots


# Versions and configuration

OS: Windows
OS Version: 10.0 2004
Game Version: df08e8d [64-bit]
Graphics Version: Tiles
Game Language: System language []
Mods loaded: [
Dark Days Ahead [dda],
Disable NPC Needs [no_npc_food],
Bionic Professions [package_bionic_professions]

# Additional context

I tested with other vehicles
Things that floated electric bicycle, mountain bike, bicycle.
Things that did not float motorcycle, motocross bike, beetle, cube van, unicycle, children's tricycle.

Start by reproducing the tow-cable scenario described: tow an electric bicycle, mountain bike, or bicycle over deep water using an amphibious truck, then compare it with the listed vehicles that sink. No source file or test is named; done means bicycles sink when towed over deep water while preserving normal behavior after returning to shallow water.

Written by the indexing model from the issue text.