test_incorrect_assignment_aggregation still has an xfail

[inducer]

Cf. #78 (#80, #81).

grudge/test/test_grudge.py

Lines 1172 to 1173 in b469c86

	# FIXME, cf. https://github.com/inducer/grudge/pull/78/
	pytest.param(3, marks=pytest.mark.xfail)

(The most likely scenario is that this will just get closed when the symbolic stuff is removed, but who knows. It's worth tracking until then.)

cc @alexfikl