windowManager: Don't move sticky windows when inserting workspace

Inserting a workspace is implemented by appending a new workspace, then shifting all windows after the "new" workspace up. This has an unintended side effect on sticky windows, as changing its workspace will unstick it.

Fix this by excluding sticky windows - there's little point in moving them anyway, given that they should be on all workspaces (including the original workspace and the target one).

Note I switched to Silverblue last week and haven't figured out how to jhbuild-run gnome-shell yet, so I couldn't test the patch. run a jhbuild wayland session, but the patch works on X11.

Fixes: #1151 (closed)