As logo of the jam is under cc-by-sa4 simple logic say that the covers must be under the same license... But ok, just mention that in corner is the logo of the jam...
Viewing post in Haunted chest for platform games (Asset Pack) jam comments
I thought it was a good idea to identify that it was made for a jam, I was even going to put the logos on the covers of the games I made for other jams too. I even thought about adding “Submitted to” and a arrow pointing to the logo. Something like the covers of N64 games. Do you suggest removing it?
Idea of identification isn't bad at all. But the license of is "strict". In general you didn't made any modifications to the logo and it is there in general as a identification mark so I even can't say it is derivative in any form but license (CC-BY-SA-4.0) requires credits so if there in description would be link and explanation the corner image is a logo of "that" jam and it is under that license...