
The code was not changed when switching from gkbd-keyboard-display which
was using tab to separate layout and variant. Tecla uses '+' instead.
This fix was suggested by Neil Mayhew.
Fixes: 04aaa4b67
("keyboard: Spawn "tecla" to show keyboard map")
Closes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/7638
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3324>