Avoid iterating twice in `zipTyEnv` (#18535)
The initial version used a zipEqual
not a zip, this MR only uses a naive zip (no list length comparison), but I don't see any reason to use a zipEqual. If the zipEqual is preferred I'll put the msg back to get a better error message.
(Also, this is my first PR to GHC, so please let me know if I'm not doing it right ... !)