test: drop python3-opencv dep and set QT_XCB_GL_INTEGRATION=xcb_egl

Ubuntu 24.04 rip-and-test runs hit a qtvcp segfault after the log-
permission fix let qtvcp get further than Phase 1 had. Debian
package-arch passes the same code. Two known asymmetries match:

- python3-opencv on Ubuntu pulls Qt5 GUI bits whose cv2/qt/plugins
  directory overrides the system PyQt5 platform plugin path under
  xvfb (opencv-python issue #572, Qt Forum 119109). qtvcp's
  camview_widget tolerates ImportError on cv2 and just logs a
  warning, so dropping the dep restores the harmless fallback path
  Phase 1 was already exercising.
- xcb_glx is the historical fragile integration under xvfb
  (Launchpad #1761708, QTBUG-67537); xcb_egl is what software-GL
  stacks expect anyway. Set as defense in depth.

Local 4/4 still green with both changes.

Author: grandixximo

debian/control.top.in

@@ -58,7 +58,6 @@ Build-Depends:
     python3-dbus.mainloop.pyqt5 <!nocheck>,
     python3-qtpy <!nocheck>,
     python3-zmq <!nocheck>,
-    python3-opencv <!nocheck>,
     python3-cairo <!nocheck>,
     python3-gi <!nocheck>,
     python3-gi-cairo <!nocheck>,

tests/ui-smoke/_lib/launch.sh

@@ -43,6 +43,10 @@ export GALLIUM_DRIVER=llvmpipe
 export QT_QUICK_BACKEND=software
 export QSG_RHI_BACKEND=software
 export QT_OPENGL=software
+# Dodge a long-known xcb_glx integration crash that hits QtWebEngine
+# and related Qt5 widgets under xvfb (Launchpad #1761708, QTBUG-67537).
+# Forces the egl path which is what software-GL stacks expect anyway.
+export QT_XCB_GL_INTEGRATION=xcb_egl
 
 # Silence audio: xvfb covers X but not sound. Demote every Gst
 # Audio/Sink and disable canberra/SDL/pulse/ALSA-default paths.