x11-toolkits/como: Fix build with Qt 6.10.3+

Resolve name shadowing conflict with the QPA 6.10.3+ API.

Qt 6.10.3 added an OffscreenSurface enum to the QPlatformIntegration
class which shadows the OffscreenSurface class.

MFH: 2026Q2
With hat: kde@

(cherry picked from commit db7e2ef53948c888398c192de77bcaf2cc38399c)