Cannot use <shift> to change IM in GNOME applications

[Lily White <lilywhite2005@outlook.com>]

Hi.

I found that I can't use <shift> key (only pressing <shift> once) to 
change input methods within IBus. However, this is only reproduced in 
GNOME apps, only reproduced on Wayland, and does not affect any other 
use case.

By GNOME apps, this means pure GNOME-native apps. That is, `gtk-4-demo' 
does not fail. Other Gtk-backend apps does not fail.

And, the failing operation is using shift to toggle between languages 
within one input method (that is, it is configured within IBus settings, 
not System Settings).

Anyone who met a similar problem?