Better error message for mismatched dict key type (#22231)
Summary:
](https://our.intern.facebook.com/intern/diff/15993936/)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22231
Pulled By: driazati
Differential Revision: D15993936
fbshipit-source-id: 6822ef01477a3b32beb8c037a621fa71abd022c8
