[Bug] git diff assumes executable permissions change is always 0755

[Wes Hurd <13hurdw@xxxxxxxxx>]

git 2.24.0
macOS 10.14.6

To reproduce:
 - Start a file, commit in git
 - chmod 0744 file.txt
 - git diff
 - ls -l file.txt

git diff reports :
old mode 100644
new mode 100755

expected:
git lists actual permissions of file
new mode 100744
File's permissions are 0744 (-rwxr--r--)

Thanks,