Fix deprecation warnings coming from np.asarray

[kp992]

Fix deprecation warnings coming from np.asarray.
Related to #723

[coveralls]

coverage: 93.032%. remained the same
when pulling dc7e6cd on kp992:i723
into d7c2f52 on QuantEcon:main.

[oyamad]

@kp992 Thanks, but this doesn't fix the issue: https://github.com/QuantEcon/QuantEcon.py/actions/runs/8183575000/job/22376624643?pr=726#step:8:76

As the message says, create an ndarray with dtype=object here

QuantEcon.py/quantecon/markov/tests/test_core.py

Lines 587 to 590 in d7c2f52

	def test_raises_non_homogeneous_state_values():
	P = [[0.4, 0.6], [0.2, 0.8]]
	state_values = [(0, 1), 2]
	assert_raises(ValueError, MarkovChain, P, state_values=state_values)

and here

QuantEcon.py/quantecon/tests/test_graph_tools.py

Lines 291 to 294 in d7c2f52

	def test_raises_non_homogeneous_node_labels():
	adj_matrix = [[1, 0], [0, 1]]
	node_labels = [(0, 1), 2]
	assert_raises(ValueError, DiGraph, adj_matrix, node_labels=node_labels)