Bug summary

When using matplotlib.colorbar.make_axes function, plt.close() does not clear the new colorbar axes from memory. Tested for the Qt5 backend only. Maybe related to #22002, at least in the sense that I see no leak for Qt5 when no colorbar axes are added.

Code for reproduction

%pylab qt5
from matplotlib import colorbar
import psutil
import gc

p = psutil.Process()
for i in range(5):
    fig, ax = plt.subplots(1,1)
    ax.imshow(random.normal(size=(100,100)))
    cax = colorbar.make_axes(ax)
    plt.savefig("test.png")
    plt.pause(0.1)
    plt.close(fig)
    del fig
    del ax
    del cax
    gc.collect()
    print(p.memory_full_info().uss/1e6)

Actual outcome

250.744832
255.209472
259.514368
264.13056
268.099584

Expected outcome

Constant memory usage, as is when the line
cax = colorbar.make_axes(ax)
is commented out.

Additional information

No response

Operating system

Windows

Matplotlib Version

3.4.2

Matplotlib Backend

Qt5Agg (PyQt)

Python version

3.7.6

Jupyter version

No response

Installation

from source (.tar.gz)