fix: add eslint-plugin-github and fix lint errors

[lukekarrys]

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[lukekarrys]

@kendallgassner as we talked about in office hours, I changed this element back to a <div aria-hidden="true"> and removed the aria-label since it is only being used as an invisible scroll handler.

I was also able to add a <code></code> element around the actual code block.

Here is a link to the relevant portion of the diff: https://github.com/npm/documentation/pull/714/files#diff-a937b27cceec7399880913557eacdd40b952463cbbdd2a10ffed757124437a8eR57-R66 Does that look good to you?