.github: Make it more clear that RN must be removed
.github: Make it more clear that RN must be removed

The release-notes section must either exist with a valid release note,
or be removed (so that the relnotes script pulls the PR title). If it
exists with the dummy text, then the relnotes script will populate the
release notes with this nonsense text instead of the PR title.

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

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