Do not try to raise a Plasma::Dialog which is a dock window

For a dock window the raise does not make much sense. A window manager
raises it anyway above most windows to get it into the dock layer. But
the raise can cause quite some side effects. KWin is setting demands
attention state in that case resulting in e.g. the notification window
having demands attention set. This conflicts with the general demands
attention handling like for example a chat window demanding attention and
emitting a notification at the same time.

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