Fix image reference bug

[joepeeples]

Follow up fix for image reference bug introduced in #6051.

The bug doesn't manifest in the main branch, but will become a problem for future backport branches created off of main. I noticed this in the backport PRs #6051 and #6093 and fixed the errors in those PRs, but then realized that the problem might re-emerge again any time another backport branch gets created.

The problem is that the images/icons subdirectory won't exist for those ESS-only backport branches, because the location only exists in serverless docs.

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