change back to unix and set serial for visual test

Author: mohanrajpac

.github/workflows/e2e.yml

@@ -7,7 +7,7 @@ on:
 jobs:
     test:
         timeout-minutes: 60
-        runs-on: macos-13
+        runs-on: ubuntu-latest
         strategy:
             fail-fast: false
         env:

tests/e2e/visual-comparison.spec.ts

@@ -8,6 +8,8 @@ import {
 	deleteAllFlags,
 } from './helper';
 
+test.describe.configure({ mode: 'serial' });
+
 test.describe('Visual tests', () => {
 	test.use({ storageState: process.env.WP_AUTH_STORAGE });