.github: Improve digest formatting in workflow
.github: Improve digest formatting in workflow

This just adjusts the formatting slightly to follow the digest formats
that we have used to report recent releases. Cosmetic only.

Signed-off-by: Joe Stringer <16a9a54ddf4259952e3c118c763138e83693d7fd@cilium.io>

tgraf/cilium,michi-covalent/cilium,tgraf/cilium,tgraf/cilium,cilium/cilium,tgraf/cilium,cilium/cilium,cilium/cilium,tklauser/cilium,michi-covalent/cilium,tklauser/cilium,michi-covalent/cilium,tgraf/cilium,tklauser/cilium,tklauser/cilium,tgraf/cilium,michi-covalent/cilium,cilium/cilium,michi-covalent/cilium,tklauser/cilium,cilium/cilium