DOC: Fix heading capitalization in doc/source/whatsnew - part5 (#32550)
-Quite a lot of complicated issues here, need reviewing. Such as 'Groupby' transformed to 'GroupBy', 'I/O' to 'IO', and some others.

- [ ] Modify files v0.18.0.rst, v0.18.1.rst, v0.19.0.rst, v0.19.1.rst, v0.19.2.rst, v0.20.0.rst, v0.20.2.rst, v0.20.3.rst, v0.21.0.rst,  v0.21.1.rst

-File v0.20.0.rst has bad file name as it is actually talking about version v0.20.1.rst
> Looks good; a few minor nits

Ok changes made as requested. <samp>
Commenter does not have sufficient privileges for PR 33568 in repo pandas-dev/pandas<br>

</samp> @jbrockmendel @WillAyd  I made the change I don't understand what is going wrong during the checks > Thanks @cleconte987 nice work. The CI is green, I guess you already fixed the problems you mentioned.

No I just merged master and pushed, updated PR, and it worked this time. It happened several times that checks failed and I have no idea why it happens. Maybe server issues, server load or server busy I don't understand why is it failing. Thanks @cleconte987 