Update flatpak to 1.6.2 in Focal

[AsciiWolf]

Please, update the flatpak package in Ubuntu 20.04 to a recently released version 1.6.2.

"Due to a combination of some behaviour in flatpak and recent versions of ostree we at some point lost the use of deltas for the initial install case, instead always falling back to a full ostree operation which is a lot less efficient for pulls with many small files like a runtime. This caused some very slow installs from e.g. flathub, so I recommend everyone update to this version to get better install performance."
(See: https://github.com/flatpak/flatpak/releases/tag/1.6.2)

[Hans Joachim Desserud (hjd)]

Looks like this was updated already :) https://bugs.launchpad.net/ubuntu/+source/flatpak/1.6.2-1