Bad hint at exercises/functions/functions4.rs

[MatthiasBart]

rustc --version -> 1.77.2
rustlings --version -> 5.6.1
ls -la --> i guess for this not needed
Your OS name and version -> macOS Sonoma 14.0

The hint of this exercise suggests to make the argument price unsigned:

Also: Did you figure out that, technically, u32 would be the more fitting type
for the prices here, since they can't be negative? If so, kudos!

which leads, to either error prone casting or making also the return type u32 which is also not a good idea for results of a subtraction.

I just wanted you to make you aware of this, if you consider this as 'not so bad' then close this issue and ignore it.