Sometimes`get_notification_item` for invite notifications returns `403 FORBIDDEN` error

Here is a log of the error.
This does not happen consistently, but only some times, and only for invite notifications.
Here is a log of the error:

`the server returned an error: [403 / M_FORBIDDEN] User @mauro.romito:matrix.org not in room !rWncTinLEtLXDzUGge:element.io, and room previews are disabled
`

Seems that this happens when trying to fetch the room given its room id from the client in the function.

Start by tracing the get_notification_item function and the room fetch mentioned in the report, using the recorded M_FORBIDDEN error as the reproduction signal. Determine why invite notifications can fetch a room when the user is not a member, then verify that invite notifications no longer produce this 403 error while other notification types remain unaffected.

Written by the indexing model from the issue text.