fix(ci): grant actions write permission to poll-upstream workflow

The automatic GITEA_TOKEN lacks actions:write by default, causing
a 422 when dispatching the build-release workflow.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.gitea/workflows/poll-upstream.yml

@@ -5,6 +5,9 @@ on:
     - cron: "*/1 * * * *"
   workflow_dispatch: {}
 
+permissions:
+  actions: write
+
 jobs:
   check:
     runs-on: fedora