Use subsumes to replace equal check in an assert check in VolcanoPlanner...

In VolcanoPlanner.changeTraitsUsingConverters(), the code uses equal to check if the converted RelNode has the required trait.

if (rel != null) {
        assert rel.getTraitSet().contains(toTrait);
        ....
}

This assert check should in stead use subsumes(), since as long as the converted RelNode's trait subsumes toTrait, it would be good enough to have this converted RelNode.

Please take a look to see if there is any issue for this fix.