Use xvfb-run directly

.github/workflows/ci.yaml

@@ -114,6 +114,10 @@ jobs:
       with:
         node-version: 12.x
 
+    - name: Install xvfb
+      if: matrix.os == 'ubuntu-latest'
+      run: sudo apt-get install -y xvfb
+
     - run: npm ci
       working-directory: ./editors/code
 
@@ -124,11 +128,17 @@ jobs:
     - run: npm run lint
       working-directory: ./editors/code
 
-    - name: Run vscode tests
-      uses: GabrielBB/xvfb-action@v1.6
+    - name: Run VS Code tests (Linux)
+      if: matrix.os == 'ubuntu-latest'
+      env:
+        VSCODE_CLI: 1
+      run: xvfb-run npm test
+      working-directory: ./editors/code
+
+    - name: Run VS Code tests (Windows)
+      if: matrix.os == 'windows-latest'
       env:
         VSCODE_CLI: 1
-      with:
       run: npm test
       working-directory: ./editors/code