[Reg 6.2 -> 6.5+] Qt 3D SceneLoader memory leak again

QTBUG-61856 was reportedly fixed back in Qt 5.9. However, the leak seems to be back in Qt 6.5/6.6. Qt 6.2.11 seems unaffected.

 Steps to reproduce

1. Open Windows Task Manager
2. Build and run the reproducer project attached to QTBUG-61856 (you'll need to set the environment variable QSG_RHI_BACKEND="opengl" to test Qt 6.2 on Windows/macOS; setting this variable has no effect on the test outcome for Qt >=6.5)
3. Watch the amount of memory consumed by sceneloader-leak.exe ( as reported by Task Manager)

Expected outcomes
RAM usage fluctuates around a steady-state level indefintiely

Actual outcomes
RAM usage grows over time: <200MB at the first load, ~700 MB after 20 minutes (around 240 load+unload cycles) in Debug mode