From 2.x to 4.x, part 3: Wheels 3.x to 4.1 with wheels upgrade check

[wheels-bot[bot]]

New post: Pass 2: 3.x to 4.1 with wheels upgrade check — reading the real wheels upgrade check output before and after, why to run it before swapping vendor/wheels, and the commits that finish the move to 4.1.2.