Update po_translatable_pages for Tails 4.0

On each release n of Tails 3.0, 4.0, etc. po_translatable_pages should be updated to disable translations of news/version_* for release n-2.

Also create a ticket for Tails 5.0.

Feature Branch: puppet-tails:12483-update-po_translatable_pages, web/12483-update-po_translatable_pages

Original created by @sajolida on 12483 (Redmine)

Edited Nov 22, 2019 by intrigeri

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