Ratings: Votes are being cast against tracking revision

[d-loose]

The ratings model uses the latest revision from the tracking channel when casting a vote. This means if there's a pending update for a given snap that hasn't been installed yet, the data sent to the ratings backend will contain the revision of the pending update rather than the one locally installed.

Discovered this while adding some debugging information:

flutter: INFO ratings_model: Casting vote: VoteStatus.up for snap: 3wdHCAVyZEmYsCMFDE9qt92UV8rC8Wdk, revision: 4483

$ snap info firefox
name:      firefox
summary:   Mozilla Firefox web browser
publisher: Mozilla✓
store-url: https://snapcraft.io/firefox
contact:   https://support.mozilla.org/kb/file-bug-report-or-feature-request-mozilla
license:   unset
description: |
  Firefox is a powerful, extensible web browser with support for modern web application
  technologies.
commands:
  - firefox
  - firefox.geckodriver
snap-id:      3wdHCAVyZEmYsCMFDE9qt92UV8rC8Wdk
tracking:     latest/stable
refresh-date: 4 days ago, at 18:24 CEST
channels:
  latest/stable:    127.0.2-1     2024-06-26 (4483) 281MB -
  latest/candidate: 127.0.2-1     2024-06-26 (4483) 281MB -
  latest/beta:      128.0b6-1     2024-06-21 (4466) 281MB -
  latest/edge:      129.0a1       2024-06-26 (4485) 300MB -
  esr/stable:       115.12.0esr-1 2024-06-11 (4373) 256MB -
  esr/candidate:    115.13.0esr-1 2024-06-21 (4461) 256MB -
  esr/beta:         ↑                                     
  esr/edge:         ↑                                     
installed:          127.0.1-1                (4451) 281MB -