devel/git: Update to 2.4.0

Changelog at https://github.com/git/git/blob/master/Documentation/RelNotes/2.4.0.txt.

This update fixes a long-standing problem with git rebase of some
(but not all) merges from the vendor branch, resulting in subsequently
rebased files being placed into the root of the repo tree.

PR: 270222
Submitted by: cy
Reported by: cy
Approved by: garga