Enforce Signed-off-by for pr from Github web interface

[Ansuel Smith]

Github introduced a new option to enforce user that submit
pr from the Github web interface to include a Signed-off-by tag.

While probably 99% a pr generated from the Github web interface
is wrong and will require additional changes, at least alert the user
that he is not doing something right and to recheck.
Hoping this will prevent such a case, I have enabled the option.

This is the article [1] on how it does work.

[1] https://github.blog/changelog/2022-06-08-admins-can-require-sign-off-on-web-based-commits/