dirstate-cext: properly invalidate mtime and data in `set_untracked`

This was forgotten about in the initial implementation and was revealed while
adding the `dirstate-v2` variant of `test-issue660.t`. Neither the existing
Python implementation nor the upcoming Rust implementation suffer from this
bug since they respectively have `None` and `Option<T>` to represent the lack
of information.

Differential Revision: https://phab.mercurial-scm.org/D12414

mercurial/cext/parsers.c

@@ -517,6 +517,8 b' static PyObject *dirstate_item_set_track'
 static PyObject *dirstate_item_set_untracked(dirstateItemObject *self)
 {
 	self->flags &= ~dirstate_flag_wc_tracked;
+	self->flags &= ~dirstate_flag_has_meaningful_data;
+	self->flags &= ~dirstate_flag_has_mtime;
 	self->mode = 0;
 	self->size = 0;
 	self->mtime_s = 0;