Make the button in the 403 page Pajamas-compliant

What does this MR do and why?

Makes the button in the 403 page Pajamas-compliant.

Addresses #363979 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

It's not easy to find a 403 page, since they most often end up being 404s, so it's probably easiest to force it.

1. Apply this patch
2. Visit http://gdk.test:3000/gitlab-org/gitlab-test/-/security/configuration

MR acceptance checklist

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