Only send UpdateBufferFile messages for buffers whose files have changed

Send that message when saving a buffer as a new path.

crates/project/src/project_tests.rs

@@ -2482,7 +2482,6 @@ async fn test_buffer_is_dirty(cx: &mut gpui::TestAppContext) {
             buffer.version(),
             buffer.as_rope().fingerprint(),
             buffer.file().unwrap().mtime(),
-            None,
             cx,
         );
     });