Update upgrade branch config

As explained in f2100830 RPi4 had a different layout with not enough space
to perform kernel updates. Unfortunately this was properly fixed after the
release of v2023.5 so, to in order to perform the test use a different image
which has been published only for this purpose, which is based on v2023.5
but with the new layout.

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>