ci: use single thread for e2e tests on ci

Author: yyx990803

vitest.e2e.config.ts

@@ -3,6 +3,11 @@ import config from './vitest.config'
 
 export default mergeConfig(config, {
   test: {
+    poolOptions: {
+      threads: {
+        singleThread: !!process.env.CI,
+      },
+    },
     include: ['packages/vue/__tests__/e2e/*.spec.ts'],
   },
 })