re-up concurrent uploads

As long as it's below 20, we seem to be fine.

src/local.rs

@@ -83,7 +83,7 @@ impl LocalServer {
                 .build()
                 .unwrap(),
             tasks: JoinSet::new(),
-            semaphore: Arc::new(Semaphore::new(1)),
+            semaphore: Arc::new(Semaphore::new(10)),
         })
     }