A release event runs the workflow as it was at the tag, so re-running a
failed announcement repeats the failure even after main is fixed. A manual
run takes the tag and uses main's workflow; the action already accepts it.
announce.yml runs coffey-labs/actions discourse-release on every published
release, posting it to this project's Announcements category on
community.coffeylabs.org. The release workflow also announces
from its own job, since a release made with the job token fires no
'on: release' workflow in Gitea.