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 [Martyn Welch: Backported to v2024] Signed-off-by: Martyn Welch martyn.welch@collabora.com