Spawn worktree scanning on the scoped pool

Co-Authored-By: Brooks Swinnerton <934497+bswinnerton@users.noreply.github.com>

zed/src/worktree/worktree.rs

@@ -74,7 +74,7 @@ impl Worktree {
 
         {
             let tree = tree.clone();
-            std::thread::spawn(move || {
+            ctx.app().scoped_pool().spawn(move || {
                 if let Err(error) = tree.scan_dirs() {
                     log::error!("error scanning worktree: {}", error);
                 }