Download page is not refreshed when verification extension is installed

See the end of the screencast in attachment (originally for #14922 (closed)). The issue is still here after reverting #14922 (closed).

Elevated since it’s a regression on the download procedure.

Also document to check that in the manual test suite, section “Tails Verification” since that was missed apparently…

Original created by @sajolida on 16078 (Redmine)

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