CI: jedi v0.18.0 breaks a number of ipython test_tab_complete_warning tests

[moink]

It looks like jedi version 0.18.0 was released yesterday and broke the following tests:

FAILED pandas/tests/arrays/categorical/test_warnings.py::TestCategoricalWarnings::test_tab_complete_warning
FAILED pandas/tests/frame/test_api.py::TestDataFrameMisc::test_tab_complete_warning[DataFrame]
FAILED pandas/tests/frame/test_api.py::TestDataFrameMisc::test_tab_complete_warning[Series]
FAILED pandas/tests/indexes/test_base.py::TestIndex::test_tab_complete_warning
FAILED pandas/tests/resample/test_resampler_grouper.py::test_tab_complete_ipython6_warning

in the Linux py38_Locale pipeline only.

I have looked into it and it seems that it is caused by this commit which is part of version 0.18.0 of Jedi
davidhalter/jedi@abb2250

Ipython has a commit that I believe will fix the error:
ipython/ipython@dcd9dc9
but it's slated for inclusion in version 8.0 of ipython:
ipython/ipython#11816
(version 7.19.0 is the most recent release, on 2020-10-30)

It's causing failures in all PRs that were submitted today (2020-12-26) starting with #38696

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

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[jreback]

ok let's just pin for now (and leave this issue open to revert when it's fixed)

love for a PR