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/admin.rs

@@ -469,7 +469,7 @@ async fn deauth_user(user_id: UserId, _token: AdminToken, conn: DbConn, nt: Noti
 
     if CONFIG.push_enabled() {
         for device in Device::find_push_devices_by_user(&user.uuid, &conn).await {
-            match unregister_push_device(&device.push_uuid).await {
+            match unregister_push_device(device.push_uuid.as_ref()).await {
                 Ok(r) => r,
                 Err(e) => error!("Unable to unregister devices from Bitwarden server: {e}"),
             };