discourse-release: announce a given tag, for releases made by the job's own token

Gitea starts no workflow for events caused by the Actions bot, so a release
created with GITHUB_TOKEN never fires 'on: release'. With 'tag:' the action
fetches that release itself; drafts are skipped.

discourse-release/action.yml

@@ -11,6 +11,14 @@ inputs:
     description: optional Discord webhook URL; when set, the announcement is also posted there
     required: false
     default: ""
+  tag:
+    description: >-
+      announce the release with this tag instead of the triggering release
+      event. Needed in a workflow that creates its release with the job's own
+      token: Gitea does not start workflows for events the Actions bot causes,
+      so `on: release` never fires for those releases.
+    required: false
+    default: ""
   forum:
     description: forum base URL
     required: false
@@ -25,6 +33,8 @@ runs:
         FORUM: ${{ inputs.forum }}
         REPO: ${{ github.repository }}
         EVENT_PATH: ${{ github.event_path }}
+        TAG: ${{ inputs.tag }}
+        GITEA_TOKEN: ${{ github.token }}
         ACTION_PATH: ${{ github.action_path }}
         MAP: ${{ github.action_path }}/release-map.json
       run: |