fix: AnnouncementCollatorApi iterable error

[gaelgoth]

This time I tested it on my instance. Collector successfully fetched announcements.

[1] 2023-10-27T09:22:37.744Z search info Collating documents for announcements via AnnouncementCollatorFactory type=plugin documentType=announcements
[1] 2023-10-27T09:22:37.745Z search info indexing announcements type=plugin
[1] 2023-10-27T09:22:37.767Z backstage info ::ffff:127.0.0.1 - - [27/Oct/2023:09:22:37 +0000] "GET /api/announcements/announcements HTTP/1.1" 200 205 "-" "node-fetch/1.0 (+https://github.com/bitinn/node-fetch)" type=incomingRequest
[1] 2023-10-27T09:22:37.770Z search debug got 1 announcements type=plugin
[1] 2023-10-27T09:22:37.770Z search debug mapping announcement 8541a1dc-2725-4c79-a367-dc91bd43282b to indexable document type=plugin
[1] 2023-10-27T09:22:37.779Z search info Collating documents for announcements succeeded type=plugin documentType=announcements
[1] 2023-10-27T09:22:37.782Z backstage debug task: search_index_announcements will next occur around 2023-10-27T11:32:37.780+02:00 type=taskManager task=search_index_announcements

[kurtaking]

I cross-referenced as you did and things look good 👍🏼 Thank you for your contribution!