I have the exact same issue on a fresh install of Qubes 4.2.
The first thing i ran after updating dom0 was install contrib and now I get the same error every time i use qubes-dom0-update and i cannot install anything from contrib. The other repos still work fine.
Since the contrib repository for r4.2 is still empty, I guess it might be necessary to open an issue on Github and report it.
r4.1 repository contains the contrib packages. So either cobtrib packages for r4.2 are missing by mistake or they have been dropped deliberately. cc. @adw
Since Screenshot tool was the main subject of the user complains and it is being moved to main repo (according to Unman), it might not be necessary to open a new Github issue. I am not sure about the rest (qubes-contrib-configs, qubes-tunnel, qubes-desktop-linux-i3-gaps, qubes-rofi, qubes-remote-desktop, qubes-qmenu, qubes-polybar) as I do not use them personally, So it might be better to wait for any user/maintainer/contributor complain on them missing before opening an issue.
p.s. BTW, I see @rustybird contributed to one of those repositories.