Testing on GitHub times out because of blocked plotting functions

[WenjieDu]

Issue description

Testing action failed on GitHub Windows and MacOS platforms, e.g. https://github.com/WenjieDu/PyPOTS/actions/runs/8246332478

This is probably caused by plotting functions in https://github.com/WenjieDu/PyPOTS/blob/main/pypots/utils/visual/data.py invoked in tests/utils/visual

PyPOTS/tests/utils/visual.py

Lines 17 to 31 in 3f120e8

	class TestVisual(unittest.TestCase):
	locf = LOCF()
	imputed_test_set = locf.predict(TEST_SET)
	imputed_X = imputed_test_set["imputation"]
	X_with_missingness = TEST_SET["X"]
	X_ori = TEST_SET["X_ori"]
	def test_plot_data(self):
	plot_data(self.X_with_missingness, self.X_ori, self.imputed_X, sample_idx=10)
	def test_plot_missingness(self):
	plot_missingness(self.X_with_missingness, max_step=24, sample_idx=10)
	plot_missingness(
	~np.isnan(self.X_with_missingness[10]), max_step=24, sample_idx=10
	)