Revise browser command syntax for Pest tests

Fixed typo. This is the output when following the official docs
```
 The "--browser" argument requires a value. Usage: --browser <browser-type> (e.g., chrome, firefox, webkit).
```

```
--browser firefox 
```

Author: LorenzoSapora

browser-testing.md

@@ -96,8 +96,8 @@ test('example', function () {
 By default, the `visit()` method uses Chrome as the browser. However, if you want to use a different browser, you can specify it using the `--browser` option when running the tests:
 
 ```bash
-./vendor/bin/pest --browser=firefox
-./vendor/bin/pest --browser=safari
+./vendor/bin/pest --browser firefox
+./vendor/bin/pest --browser safari
 ```
 
 If you wish to use a different browser by default without specifying it in the command line, you can set it in your `Pest.php` configuration file: