Normalize width of key next to backspace in input-keyboard icon

[waldyrious]

The width of the key next to the backspace in input-keyboard.svg is wider than the ones to the left and under it, which doesn't match the common keyboard layouts:

This is due to pixel alignment, but perhaps that would still be possible by widening the backspace key instead.

Note: This issue was originally reported in https://github.com/elementary/icons/pull/1082#issuecomment-1027832717.