PR #35068 made Container (which GraphNode inherits) default to
MOUSE_FILTER_PASS, so I removed the manual override, but it turns out
that GraphNode's constructor still overrides it to MOUSE_FILTER_STOP.
Another fix could be to remove the STOP in the constructor, but I don't
know if it's there for a specific reason (e.g. to have GraphNodes STOP
by default, but PASS in a specific case).
Fixes#35978.