Fix workspace thumbnails box size in overview

[mzur]

The container box of the workspace thumbnails has the wrong height. This cuts off mouse events for all thumbnails but those in the first row. Effects:

• You can switch to a workspace in the first row with a click but not in the second row of workspaces.
• You can drag and drop a window in the first row but not to the second row of workspaces.

[AJCxZ0]

I've observed this in Fedora 35 with GNOME 41.1 on Wayland.

• In the workspace grid overview, switching to a workspace by double-clicking the empty (part of a) workspace only works for the top row.
  • Clicking on a window in a workspace on other rows correctly switches the that window and workspace.
• Dragging a window to a workspace only works for the top row, with windows dropped in lower workspaces appearing in the top row workspace above.

While not part of this bug, the workspace grid overview is unexpectedly small and the config offers no opportunity to scale it.

[sanwablo]

Same behaviour as described by @mzur and @AJCxZ0 and in Ubuntu 22.04 with GNOME 42.5 on X11.

[mainland]

I believe I have a fix for this issue at mainland/gnome-shell-wsmatrix@62be78e8. Since the fix is for an older version of gnome-shell (42.9), I didn't open a pull request.