fix: add sleep command and set DISPLAY environment variable for Xvfb in test workflow

Author: dermatz

.github/workflows/test.yml

@@ -26,11 +26,14 @@ jobs:
           sudo apt-get install -y xvfb
           Xvfb :99 -screen 0 1024x768x24 &
           export DISPLAY=:99
+          sleep 3
       - name: Checkout code
         uses: actions/checkout@v2
       - name: Install dependencies
         run: npm install
       - name: Compile the extension
         run: npm run compile
       - name: Run tests
+        env:
+          DISPLAY: :99
         run: npm test