bug#49971: 28.0.50; indent-tabs-mode not working globally

[Gabriel]

It seems that the new 'indent-tabs-mode' minor-mode, although defined as
global, it's working as a buffer-local minor-mode. Using emacs from
master branch built today:

1. emacs -Q
2. C-h v 'indent-tabs-mode' (value is t)
3. eval '(indent-tabs-mode -1)'
4. C-h v 'indent-tabs-mode' (local value is nil; global value is t)