Use read-only access methods for read-only entity operations (#31254)

This PR replaces some `update()` calls with either `read()` or
`read_with()` when the `update()` call performed read-only operations on
the entity.

Many more likely exist, will follow-up with more PRs.

Release Notes:

- N/A

crates/channel/src/channel_store_tests.rs

@@ -137,7 +137,7 @@ async fn test_channel_messages(cx: &mut TestAppContext) {
     let user_id = 5;
     let channel_id = 5;
     let channel_store = cx.update(init_test);
-    let client = channel_store.update(cx, |s, _| s.client());
+    let client = channel_store.read_with(cx, |s, _| s.client());
     let server = FakeServer::for_client(user_id, &client, cx).await;
 
     // Get the available channels.