.github/workflows: checkout all git history for Image GC
.github/workflows: checkout all git history for Image GC

Scruffy verifies if a commit exists in the git history before it
sets the quay.io image for garbage collection. In order to guarantee
that images from the tree are not deleted, the GitHub action needs to
have all commits of branches checked out.

Signed-off-by: André Martins <bc9800b9d52a24cce72a73dd528afed53f10e5fc@cilium.io>

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