title: Weird matplotlib contour plot axis labels shows two sets of values
body: <p>I'm using matplotlib 3.3.4 and generating a basic contour plot. But when I do so, the X and Y axis labels are showing my desired range (e.g. 0 to pi) but there's also an extra set of labels showing up that appear to be some sort of normalized values (0 to 1). The following code reproduces this:</p>
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt
  
  x = np.linspace(0, np.pi, 40)
  y = np.linspace(0, np.pi, 40)
  z = np.sin(x[:, None])**2 + np.sin(y)**2
  
  fig, ax = plt.subplots(figsize=(10,10))
  ax = fig.add_subplot(111)
  ax.contour(x, y, z)
  </code></pre>
  <p>and produces a plot like the one below. I see axis labels at the expected values [0, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0]. But there's another set [0, 0.2, 0.4, 0.6, 0.8, 1.0] that's coming from somewhere.</p>
  <p>After reviewing the contour() example at <a href="https://matplotlib.org/stable/gallery/images_contours_and_fields/contour_demo.html" rel="nofollow noreferrer">Contour Example</a> I realize I should probably be calling np.meshgrid() rather than doing the extra axis stuff to produce z above.</p>
  <p>Any clues as to what is causing this odd axis label behavior?
  <a href="https://i.stack.imgur.com/MkM1c.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/MkM1c.png" alt="enter image description here" /></a></p>