Bug report

Bug summary

Using a TextBox in current master produces a seemingly unrelated warning.

Code for reproduction

import matplotlib.pyplot as plt
from matplotlib.widgets import TextBox

fig = plt.figure()
tba = fig.add_axes([.5, .5, 0.1, 0.05])
tb = TextBox(tba, 'Input: ', initial="999")

plt.show()

Run this code, then click into the text box to change the text.

Actual outcome

Once clicked in the box, the following warning appears:

D:\***\lib\_collections_abc.py:841: MatplotlibDeprecationWarning:
The keymap.all_axes rcparam was deprecated in Matplotlib 3.3 and will be removed two minor releases later.
  self[key] = other[key]

Expected outcome

No warning.
This bisects to #16529, which introduced this warning, but supposedly not for the use case of TextBoxes.

Matplotlib version

• Operating system: Windows 8.1
• Matplotlib version: current master branch
• Matplotlib backend (print(matplotlib.get_backend())): Qt5Agg
• Python version: 3.6.4