.github: fix correct sha for images build
.github: fix correct sha for images build

This commit sets the correct tag for the images build depending on the
event type from GH actions.

Fixes: 84bc5652b7d4 (".github/workflows: cleanup images-legacy workflow")
Signed-off-by: André Martins <bc9800b9d52a24cce72a73dd528afed53f10e5fc@cilium.io>

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