FIX: use `tag` model instead of tagId property. (PR #11298)

In a recent commit https://github.com/discourse-org/discourse-teams-sidebar/commit/866fa008d4ae4ff913d8c7cd448c5dc1c556b5fb, support for tagId property is removed.

And added a test case. Follow-up for 2d5bb516a6aa035dca11dd55dfbb5b796c54c166.

GitHub

:+1: