backporting: Add set-labels commands to check-stable
backporting: Add set-labels commands to check-stable

Output the full set-labels.py one-liner command when running
check-stable to assist backporters attempting to backport. It's up to
the backporter to exclude particular PRs if the PR is not included in
the PR.

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

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