Fix unmet prerequisites help URL

What does this MR do and why?

Fixes a recently broken link:

#341354 (closed)

Screenshots or screen recordings

2021-09-22_12-43-31

How to set up and validate locally

1. Generate a build with unmet prerequisites
2. Visit the help page path

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.