Auto merge of #143294 - ChrisDenton:rename-mingw, r=Kobzol

Rename `mingw-*` CI jobs to `pr-*`

The name `mingw` confuses people because these CI jobs now do much more than just cross-compile to mingw.

This is basically a find/replace. I chose the name `pr-` because it's job is to do general PR checks,

Author: bors