kickoff/main.qml: Round backgroundMetrics
Instead of relying on the values reported by the svg's, which can be inconsistent such as 3.999999, round them to nearest integer.
This fixes issue with Kickoff calculating space for the items in the item grid view.
(cherry picked from commit 91ded110)
Co-authored-by: Akseli Lahtinen akselmo@akselmo.dev