bpo-38669: patch.object now raises a helpful error (GH17510)

This means a clearer message is now shown when patch.object is called with two string arguments, rather than a class and a string argument.
(cherry picked from commit cd90a52983db34896a6335a572d55bdda274778f)

Co-authored-by: Elena Oat <oat.elena@gmail.com>
3 files changed