[autotests] Fix PointerInputTest::testCursorImage()

Summary:
    FAIL!  : KWin::PointerInputTest::testCursorImage() Compared QImages differ in device pixel ratio.
       Actual   (((p->cursorImage()))): 2
       Expected (blueScaled): 1
       Loc: [/home/vlad/Workspace/KDE/src/kde/workspace/kwin/autotests/integration/pointer_input.cpp(1058)]

Test Plan: The test passes.

Reviewers: #kwin, davidedmundson

Reviewed By: #kwin, davidedmundson

Subscribers: davidedmundson, kwin

Tags: #kwin

Differential Revision: https://phabricator.kde.org/D27725