fix typos in mbe tests

crates/ra_ide_api/src/runnables.rs

@@ -22,7 +22,7 @@ pub enum RunnableKind {
 }
 
 pub(crate) fn runnables(db: &RootDatabase, file_id: FileId) -> Vec<Runnable> {
-    let source_file = db.parse(file_id);
+    let source_file = db.parse(file_id).tree;
     source_file.syntax().descendants().filter_map(|i| runnable(db, file_id, i)).collect()
 }