Apply ref_option lint findings (#7143)

Quote from the lint description:
"More flexibility, better memory optimization, and more idiomatic Rust code.

&Option<T> in a function signature breaks encapsulation because the caller must own T and move it into an Option to call with it. When returned, the owner must internally store it as Option<T> in order to return it. At a lower level, &Option<T> points to memory with the presence bit flag plus the T value, whereas Option<&T> is usually optimized to a single pointer, so it may be more optimal."

src/api/notifications.rs

@@ -338,7 +338,7 @@ impl WebSocketUsers {
     }
 
     // NOTE: The last modified date needs to be updated before calling these methods
-    pub async fn send_user_update(&self, ut: UpdateType, user: &User, push_uuid: &Option<PushId>, conn: &DbConn) {
+    pub async fn send_user_update(&self, ut: UpdateType, user: &User, push_uuid: Option<&PushId>, conn: &DbConn) {
         // Skip any processing if both WebSockets and Push are not active
         if *NOTIFICATIONS_DISABLED {
             return;