Upgrade to Linux 5.2+ with the Spectre v1 swapgs mitigations in Tails 4.0~beta2

Originally created by @intrigeri on #16942 (Redmine)

It’s now in sid.

Feature Branch: bugfix/16942-spectre-v1-swapgs+force-all-tests

Edited May 15, 2020 by intrigeri

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