Mark PyTraceback as ThreadSafe

vm/src/obj/objtraceback.rs

@@ -1,6 +1,6 @@
 use crate::frame::FrameRef;
 use crate::obj::objtype::PyClassRef;
-use crate::pyobject::{PyClassImpl, PyContext, PyRef, PyValue};
+use crate::pyobject::{PyClassImpl, PyContext, PyRef, PyValue, ThreadSafe};
 use crate::vm::VirtualMachine;
 
 #[pyclass]
@@ -11,6 +11,7 @@ pub struct PyTraceback {
     pub lasti: usize,
     pub lineno: usize,
 }
+impl ThreadSafe for PyTraceback {}
 
 pub type PyTracebackRef = PyRef<PyTraceback>;