DOC/BUILD: failing on master

[jreback]

/home/runner/work/pandas/pandas/doc/source/whatsnew/v1.4.0.rst:372: WARNING: Inline interpreted text or phrase reference start-string without end-string.
/home/runner/work/pandas/pandas/doc/source/whatsnew/v1.4.0.rst:372: WARNING: Inline interpreted text or phrase reference start-string without end-string.

see this CI output