0e917c3dbf
`ThumbnailsBox` listens for the `showing` signal from the `Overview` to create its thumbnails and destroys them on the `hide` signal. Since the `showing` signal can be emitted multiple times when switching between the shown and hidden state without ever fully completing the transition, this will cause `_createThumbnails` to be called multiple times, each time adding another set of workspaces. Fixes: https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/3819 Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1828>