Hiding the `WorkspacesDisplay` triggers a reallocation of the
`ControlsManagerLayout` which can fail with the following error:
```
JS ERROR: TypeError: workspace is undefined
_getSpacing@resource:///org/gnome/shell/ui/workspacesView.js:229:13
vfunc_allocate@resource:///org/gnome/shell/ui/workspacesView.js:355:18
vfunc_allocate@resource:///org/gnome/shell/ui/overviewControls.js:200:33
vfunc_hide@resource:///org/gnome/shell/ui/workspacesView.js:1070:38
vfunc_unmap@resource:///org/gnome/shell/ui/overviewControls.js:672:33
hideOverview@resource:///org/gnome/shell/ui/layout.js:312:28
_hideDone@resource:///org/gnome/shell/ui/overview.js:617:32
onComplete@resource:///org/gnome/shell/ui/overview.js:390:37
_makeEaseCallback/<@resource:///org/gnome/shell/ui/environment.js:134:13
_easeActorProperty/<@resource:///org/gnome/shell/ui/environment.js:298:60
```
This can be reproduced by closing the overview with the three-finger
gesture.
Thus propagate the unmap before hiding the `WorkspacesDisplay`.
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2088>
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