Remove reference to external GH action for xvfb

Author: darkriszty

.github/workflows/test.yml

@@ -25,6 +25,7 @@ jobs:
 
     - run: npm ci
 
-    - uses: GabrielBB/xvfb-action@v1
-      with:
-        run: npm test
+    - run: xvfb-run -a npm test
+      if: runner.os == 'Linux'
+    - run: npm test
+      if: runner.os != 'Linux'