GUID normalisation bug, leading to duplicates

Hello,
This plug-in is performing an hardcoded URL normalisation of GUIDs from `https://` to `http://`:

https://github.com/Automattic/pushpress/blob/0b6c4f34ce06c01d66eeccf6ae27cd6950f4f31e/class-pushpress.php#L107

But the articles themselves in the corresponding RSS feeds have GUIDs using `https://`.

This leads to duplicate in clients subscribing to those feeds because articles exist with two different GUIDs:

https://github.com/FreshRSS/FreshRSS/issues/5151#issuecomment-3303107847

At the very least, the normalisation should be made the other way around, now that a majority of WordPress blogs run HTTPS, including WordPress.org, but a better approach would be desirable.