package/git: security bump to version 2.26.3
Fixes CVE-2021-21300:
On case-insensitive file systems with support for symbolic links, if Git is
configured globally to apply delay-capable clean/smudge filters (such as Git
LFS), Git could be fooled into running remote code during a clone.
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>