Roll out git version 2.40.0
Let's start rolling out Git 2.40 since it contains some important functionality that we want to start using:
- Mailmap support in git-cat-file’s batch mode, contributed by Siddarth (GSoC contributor mentored by Chris and John).
- git-check-attr learned to take a treeish to read gitattributes from (contributed by Karthik).
Edited by John Cai