Fix side effect on saved query objects

[mhaoli]

Before this fix, in the following code example, the second line will modify the saved_query object.

saved_query = self.dut.ui(text='AAA').ancestor(res='BBB')
saved_query.child(res='ZZZZZZZZZZZZZZZZZZZ').click()
saved_query.child(text='CCC').wait.exists(3)

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This change is