Feed not found despite reasonable-looking <link rel> tag

[irons]

Using NNW 6.1.4 on macOS 13.6, I tried to add a subscription to https://cloud.google.com/kubernetes-engine/docs/release-notes, which failed with a "Feed not found" error. However, the page source, captured here, showed an atom feed:

<link rel="alternate" type="application/atom+xml" href="https://cloud.google.com/feeds/gke-main-release-notes.xml"/>

Creating a subscription to https://cloud.google.com/feeds/gke-main-release-notes.xml in NNW succeeded, so the only problem is the failure to detect it.