docs(@angular/build): correct the unit-test browsers option description

The description states that tests run with jsdom when no browsers are set and
gives 'ChromeHeadless' as the only example. The Vitest runner prefers happy-dom
when it is installed, the Karma runner uses the browsers of its configuration,
and the Vitest Playwright provider rejects 'chrome', so the example fails with
the most common provider. Describe both runners and give an example for each.

Author: MeAkib

packages/angular/build/src/builders/unit-test/schema.json

@@ -25,7 +25,7 @@
       "default": false
     },
     "browsers": {
-      "description": "Specifies the browsers to use for test execution. When not specified, tests are run in a Node.js environment using jsdom. For both Vitest and Karma, browser names ending with 'Headless' (e.g., 'ChromeHeadless') will enable headless mode.",
+      "description": "Specifies the browsers to use for test execution. When not specified, the Vitest runner runs tests in a Node.js environment using `happy-dom` if it is installed, otherwise `jsdom`, and the Karma runner uses the browsers of its configuration. Browser names ending with `Headless` enable headless mode (e.g., `ChromiumHeadless` for Vitest with the Playwright provider, or `ChromeHeadless` for Karma).",
       "type": "array",
       "items": {
         "type": "string"