plugins/vala-indenter: Fix bug and revert feature for now

Fix bug regarding the indentation and revert feature that requires GTK-Sourceview changes

The feature requires this change:

• https://gitlab.gnome.org/GNOME/gtksourceview/-/blob/2162b1ab4de5e5edf0c3667901cdd05eb8a76e59/gtksourceview/gtksourceview.c#L4110

And the bug was not caught by my unit tests in the GSV-MR