Windows: Fix canonicalize return UNC path (#11083)

In Windows platform, using notify to watch file events. 
1. in [notify windows
implement](https://github.com/notify-rs/notify/blob/3df0f65152c8585cfb29d231c880b86b9164dcfd/notify/src/windows.rs#L344),
we get the full file path, just with `path.join(file_path)`.
2. In [zed worktree
start_backgroud_scan_tasks](https://github.com/zed-industries/zed/blob/d2569afe662be93c926eed1aeb2b17d050ba90b0/crates/worktree/src/worktree.rs#L679),
`abs_path` is not unc path, so we get all file events with not unc path.
3. but in [zed worktree
process_event](https://github.com/zed-industries/zed/blob/d2569afe662be93c926eed1aeb2b17d050ba90b0/crates/worktree/src/worktree.rs#L3619),
we `strip_prefix` unc path all times, it will always print annoy error.

@mikayla-maki I can't reopen pre closed pr #10501 .

Release Notes:

- N/A

crates/worktree/src/worktree.rs

@@ -673,7 +673,11 @@ fn start_background_scan_tasks(
 ) -> Vec<Task<()>> {
     let (scan_states_tx, mut scan_states_rx) = mpsc::unbounded();
     let background_scanner = cx.background_executor().spawn({
-        let abs_path = abs_path.to_path_buf();
+        let abs_path = if cfg!(target_os = "windows") {
+            abs_path.canonicalize().expect("start background scan tasks failed for canonicalize path {abs_path}")
+        } else {
+            abs_path.to_path_buf()
+        };
         let background = cx.background_executor().clone();
         async move {
             let events = fs.watch(&abs_path, FS_WATCH_LATENCY).await;