CI: set Qt to use offscreen platform to avoid libEGL load issue

Author: Acly

.github/workflows/test.yml

@@ -31,7 +31,14 @@ jobs:
   test:
     runs-on: ubuntu-22.04
     timeout-minutes: 20
+    env:
+      QT_QPA_PLATFORM: offscreen
     steps:
+      # PyQt6.QtGui import requires libEGL.so.1 (even with QT_QPA_PLATFORM=offscreen)
+      - name: Packages
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libegl1 libgl1 libxkbcommon-x11-0
       - name: Checkout
         uses: actions/checkout@v3
         with: