test: keep headful CCTV gate rendering when occluded

changelog.d/1267-cctv-session-admission.md

@@ -1,2 +1,3 @@
 - Gate CCTV HLS media requests before session work, bind leases to the direct
   peer, and bound per-peer leases across shared sessions (asturksever, #1267).
+- Keep headful CCTV QA rendering active when its window is occluded (asturksever, #1267).

scripts/qa-cctv-v2.mjs

@@ -454,6 +454,7 @@ async function main() {
       ...(HEADFUL ? [] : ['--use-gl=angle', '--use-angle=swiftshader']),
       '--disable-dev-shm-usage',
       '--disable-web-security',
+      '--disable-backgrounding-occluded-windows',
       '--disable-background-timer-throttling',
       '--disable-renderer-backgrounding',
       '--window-size=1280,800',