Extend timeout in tst_qdeclarativetextedit::delegateLoading

On some CI machines (OS X 10.7) this test actually passes but takes
5100 ms to load the delegate.

Task-number: QTBUG-42264
Change-Id: I008cbf0e163257c800370951920384108e5a390b
Reviewed-by: Tony Sarajärvi <tony.sarajarvi@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>