ci: record the verified cancel-in-progress behaviour

Assisted-by: GLM 5.3 Flash

.gitea/workflows/test.yml

@@ -31,8 +31,9 @@ env:
   GOMAXPROCS: "2"
 
 # A superseded run of the same ref is cancelled instead of queueing behind one
-# that no longer matters. Unverified on this Gitea: this block is the experiment
-# from the roadmap, push twice in a row and watch whether the first run cancels.
+# that no longer matters. Verified on this Gitea on 2026-09-17: a queued run
+# whose ref moved on is cancelled before it ever reaches the runner, while a
+# run already dispatched there runs to completion.
 concurrency:
   group: ${{ gitea.workflow }}-${{ gitea.ref }}
   cancel-in-progress: true