CI: Doc build is failing because of upstream changes

[phofl]

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

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

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

Reproducible Example

>>>-------------------------------------------------------------------------
Warning in /home/runner/work/pandas/pandas/doc/source/user_guide/io.rst at block ending on line 3033
Specify :okwarning: as an option in the ipython:: block to suppress this message
----------------------------------------------------------------------------
/home/runner/miniconda3/envs/pandas-dev/lib/python3.8/site-packages/charset_normalizer/api.py:91: UserWarning: Trying to detect encoding from a tiny portion of (11) byte(s).
  warn('Trying to detect encoding from a tiny portion of ({}) byte(s).'.format(length))
<<<-------------------------------------------------------------------------

and

WARNING: failed to reach any of the inventories with the following issues:
intersphinx inventory 'https://www.statsmodels.org/devel/objects.inv' not fetchable due to <class 'requests.exceptions.ConnectionError'>: HTTPSConnectionPool(host='www.statsmodels.org', port=443): Max retries exceeded with url: /devel/objects.inv (Caused by NewConnectionError('<urllib3.connection.HTTPSConnection object at 0x7fef8dc72670>: Failed to establish a new connection: [Errno -3] Temporary failure in name resolution'))

[phofl]

cc @pandas-dev/pandas-core

[bashtage]

Seems to be available now.

[johnzangwill]

This is the log from this morning:
error_log.log

[bashtage]

Looks like he NumericIndex changes are biting from io.rst.