grab worker count from tokio

Author: sokra

crates/napi/src/next_api/turbopack_ctx.rs

@@ -207,6 +207,7 @@ pub fn create_turbo_tasks(
                     turbo_tasks_backend::StorageMode::ReadWrite
                 }),
                 dependency_tracking,
+                num_workers: Some(tokio::runtime::Handle::current().metrics().num_workers()),
                 ..Default::default()
             },
             Either::Left(backing_storage),