Fix setting the UAID in DbClient::update_user

It is an error to try and set the primary key of a row via UpdateItem.

autoendpoint/src/db/client.rs

@@ -80,7 +80,8 @@ impl DbClient {
     /// already exist, has a different router type, or has a newer
     /// `connected_at` timestamp.
     pub async fn update_user(&self, user: &DynamoDbUser) -> DbResult<()> {
-        let user_map = serde_dynamodb::to_hashmap(&user)?;
+        let mut user_map = serde_dynamodb::to_hashmap(&user)?;
+        user_map.remove("uaid");
         let input = UpdateItemInput {
             table_name: self.router_table.clone(),
             key: ddb_item! { uaid: s => user.uaid.to_simple().to_string() },