Bug summary

imshow rendering changed from 3.1.0 to 3.1.1 when yticks ar set.
Square matrix display is no longer square.
Note that setting xticks do not affect the display.

Code for reproduction

import matplotlib.pyplot as plt
fig, ax = plt.subplots()
ax.imshow([[1,2],[3,4]])
ax.set(yticks=[0,1])  # change the display in 1.3.1

outcome in 3.1.1

Previous outcome in 3.1.0

Matplotlib version

• Operating system: Linux
• Matplotlib version: 3.1.0 / 3.1.1
• Matplotlib backend: module://ipykernel.pylab.backend_inline
• Python version: 3.7.3