Test GNOME power management overriding of X.Org DPMS defaults

The symptoms to reproduce are described in the parent ticket.

The goal is to check if latest GNOME exposes this bug too, so one should test this on Debian unstable, or Fedora Rawhide, or whatever is close to the latest upstream stuff.

Parent Task: #5617 (closed)

Original created by @intrigeri on 6421 (Redmine)

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