[issue40876] Clarify error message in csv module

[Ram Rachum]

Change by Ram Rachum <ram at rachum.com>:


----------
keywords: +patch
pull_requests: +19873
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/20653

_______________________________________
Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40876>
_______________________________________