[Bug]: diagonal lines in pcolormesh with Gouraud shading and transparency #27016

import matplotlib.colors as m_colors
import matplotlib.pyplot as plt
import numpy as np
plt.pcolormesh(np.array([[0, 1, 2], [0, 1, 2]]),
               np.array([[0, 0, 0], [1, 1, 1]]),
               np.array([[0, 1, 2], [0, 1, 2]]),
               cmap=m_colors.LinearSegmentedColormap.from_list(
                   "", [(0, 0, 0, 0), (0, 0, 0, 1)]),
               shading="gouraud")
plt.plot()