docs: add workers for ci (#23046)

docs/src/ci.md

@@ -6,7 +6,6 @@ title: "Continuous Integration"
 Playwright tests can be executed in CI environments. We have created sample
 configurations for common CI providers.
 
-<!-- TOC -->
 
 ## Introduction
 
@@ -50,6 +49,21 @@ configurations for common CI providers.
    dotnet test
    ```
 
+## Workers
+* langs: js
+
+We recommend setting [workers](./api/class-testconfig.md#test-config-workers) to "1" in CI environments to prioritize stability and reproducibility. Running tests sequentially ensures each test gets the full system resources, avoiding potential conflicts. However, if you have a powerful self-hosted CI system, you may enable [parallel](./test-parallel.md) tests. For wider parallelization, consider [sharding](./test-parallel.md#shard-tests-between-multiple-machines) - distributing tests across multiple CI jobs.
+
+```js title="playwright.config.ts"
+import { defineConfig, devices } from '@playwright/test';
+
+export default defineConfig({
+  // Opt out of parallel tests on CI.
+  workers: process.env.CI ? 1 : undefined,
+});
+```
+
+
 ## CI configurations
 
 The [Command line tools](./browsers#install-system-dependencies) can be used to install all operating system dependencies on GitHub Actions.