v2021: lava: amd64-upsquared6000: Use release v2022.2 image on 1st stage

Task https://phabricator.apertis.org/T9138

Commit 58cf28b ("lava: amd64-upsquared6000: User a newer v2022 first
stage image") set the UP Squared 6000 1st stage image to a weekly build.
As the weekly image may get deleted sooner than later, let's use a
release point.

Signed-off-by: Ariel D'Alessandro <ariel.dalessandro@collabora.com>