In the problem condition the author suggests that passanger rest in the bus ALWAIS (for any bus stop) great or equal to zero. But tests don't check this!

I don't undestand:
arrays = [[-8, -8], [0, -6], [4, -8], [2, -4], [-2, 4], [-1, -5], [7, -2], [-5, 4]]
shift = 1
my result: [-8, -8, -2, -6, -6, 3, 2, -7, 4]
estimated result: [-8, -8, 0, -6, 4, -8, 2, -4, -2, 4, -1, -5, 7, -2, -5, 4]

Manually:
-8 -8
0 -6
4 -8
2 -4
-2 4
-1 -5
7 -2
-5 4
-8 -8 -2 -6 -6 3 2 -7 4 # as in my solution

Why estimated result is -8, -8, 0, -6, 4, -8, 2, -4, -2, 4, -1, -5, 7, -2, -5, 4 ???
Such result is correct for shift = 3

You forgot that ascii-code contains some symbols wich ascii-number less than ascii-code for digits, for example '#@%'. So, if input string will contain words with one of those symbols, your solution will work wrong.
Try this: "A9# fg1 ghji3%"

This code don't pass the test below:
[[2,4], [2,6], [2, 8]] -> [[6, 12], [4, 12], [3, 12]]
See kata condition for Bash