taskmanager: Use default WindowType in GroupDialog

Before frameworks/plasma-framework!391, PopupMenu only has the default
role, which blocks a dialog with the PopupMenu role from receiving
any QFocusEvent on Wayland.

In case frameworks/plasma-framework!391 cannot be merged, this commit
sets GroupDialog as a Normal winodw, so it's possible for GroupDialog to
receive QFocusEvent normally, and the behavior on X11 can remain the same.

BUG: 444328
2 jobs for !707 with work/fusionfuture/BUG444328-no-type in 5 minutes and 4 seconds (queued for 45 minutes and 23 seconds)
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