Duplicated access key of the prev and next buttons when prev_next_buttons_location == 'both'

[SuperPat45]

Problem

The Chrome Lighthouse auditor report some accessibility problems;
_ Color contrast problems in the lateral nav bar
_ Missing aria-label in the input search box
_ Duplicated access key of the previous and next buttons when variable theme_prev_next_buttons_location == 'both'

Reproducible Project

The first two are available in all rtd doc like: https://sphinx-rtd-theme.readthedocs.io/en/latest/
The third one need variable theme_prev_next_buttons_location == 'both'

Expected Results

Improve Chrome Lighthouse audit score

[stsewd]

Hi, thanks for the report, some of these are already reported:

• Contrast Color contrast is too low on various page elements #971
• Search bar without a label/aria-label Search input boxes lack labels #970 Match searchbox.html from upstream #1024

The third one I don't think it has been reported before.