make sure notifications are always on top

[uclaros]

According to https://doc.qt.io/qt-6/qml-qtquick-controls-popup.html#showing-non-child-items-in-front-of-popup

Fixes: #3232

[github-actions]

Pull Request Test Coverage Report for Build 8719689898

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 198 unchanged lines in 9 files lost coverage.
• Overall coverage decreased (-0.3%) to 59.96%

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Files with Coverage Reduction	New Missed Lines	%
input/app/projectsproxymodel.h	1	0.0%
input/app/attributes/attributecontroller.cpp	1	77.37%
input/app/projectsmodel.h	2	25.0%
input/core/project.h	2	55.56%
input/core/merginuserinfo.cpp	3	72.99%
input/app/projectwizard.cpp	20	2.94%
input/app/projectsproxymodel.cpp	38	0.0%
input/app/projectsmodel.cpp	65	65.75%
input/app/mmstyle.h	66	2.02%

Totals
Change from base Build 8717538064:	-0.3%
Covered Lines:	7576
Relevant Lines:	12635

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💛 - Coveralls