The testing for both the previous diff and this diff are combined here. I tested the stack so far by doing the following:
1. Finding a place to call `toggleMessagePin` on the client. For this, I used the thread settings media gallery on `web`.
2. Log into an admin account locally.
3. Call `toggleMessagePin` with the following parameters: `{messageID: "123", threadID: "83895", isPinned: false}`. I confirm that the insertion into `pinned_messages` was successful.
4. Call `toggleMessagePin` with the following parameters: `{messageID: "123", threadID: "83895", isPinned: false}`. I confirm that the deletion from `pinned_messages` was successful.
5. Log into a non-admin account part of thread 83895
6. Call `toggleMessagePin` with the same parameters, and confirm that the `ServerError` throws