fix get_job_update returning error

When get_progress specified to true, but there is no record of progress for given job
Endpoint will fail and return error.

Nothing cricial but should be fixed.

backend/windmill-api/src/jobs.rs

@@ -4663,8 +4663,8 @@ async fn get_job_update(
                 "progress_perc"
 
             )
-            .fetch_one(&db)
-            .await?
+            .fetch_optional(&db)
+            .await?.and_then(|inner| inner)
     } else {
         None
     };