CI: test failure, raises unexpected warning
I merged master into #33247 . This results in a failing test:
`pandas/tests/plotting/test_converter.py::TestRegistration::test_pandas_plots_register`

in Windows py37_np_18

```
 AssertionError: Caused unexpected warning(s): [('DeprecationWarning', DeprecationWarning("Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated since Python 3.3,and in 3.9 it will stop working")
```

Was this already detected?

[test results](https://dev.azure.com/pandas-dev/pandas/_build/results?buildId=37342&view=logs&j=ea1e4a48-f1c1-5933-c4f7-7e56de389fce&t=967459d8-2b8b-5603-ef1c-c585363eb056&l=92)