Start the merging-rebase to v2.40.1

I messed up. Via hitting the "Merge" button in
#4417, a new merge commit was
put on top, again making two "Start the merging-rebase" commits
reachable from the tip commit. The entire point of that PR, however, was
to make only one of them reachable, so that the `shears.sh` script of
https://github.com/git-for-windows/build-extra would have a chance to
make the next rebase easy.

So let's do this again. And then push directly instead of going through
a PR.

This commit starts the rebase of b799d25 to 2df31ab

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho