git-contrib: use 'git shortlog' command

git-contrib: use 'git shortlog' command

Also, this drops Weblate (again) and dependabot from the contributers list.

Moreover, this makes the contributers sorted by git command, rather
than sort command. Then, the authors are sorted by their first name, e.g.
- before
Xiaotian Wu, Yuri Chornoivan, Yu Watanabe, Zbigniew Jędrzejewski-Szmek,
- after
Xiaotian Wu, Yu Watanabe, Yuri Chornoivan, Zbigniew Jędrzejewski-Szmek,

Suggested-by: Matteo Croce <teknoraver@meta.com>