Fix bug in line mark when MARK_LINE_AT_SCAN_TIME=false (#1171)

Previously we did not mark the line for an object in
`trace_object_with_opportunistic_copy` if we leave the object in-place
when `MARK_LINE_AT_SCAN_TIME=false`.

---------

Co-authored-by: Kunshan Wang <wks1986@gmail.com>

Author: k-sareen

src/policy/immix/immixspace.rs

@@ -646,6 +646,10 @@ impl<VM: VMBinding> ImmixSpace<VM> {
                 #[cfg(feature = "vo_bit")]
                 vo_bit::helper::on_object_marked::<VM>(object);
 
+                if !super::MARK_LINE_AT_SCAN_TIME {
+                    self.mark_lines(object);
+                }
+
                 object
             } else {
                 // We are forwarding objects. When the copy allocator allocates the block, it should