docs: remove the chapter claiming that PHPUnit is automatically enabled if a...

This job performs [PHPUnit](https://docs.phpunit.de/) tests.

It is bound to the `build` stage, and is automatically enabled if a PHPUnit [XML configuration file](https://docs.phpunit.de/en/11.0/configuration.html)

is found in the project (`phpunit.xml` or `phpunit.xml.dist`).

It is bound to the `build` stage, and is enabled by default.

It uses the following variable:

It uses the following variables:

| Input / Variable | Description                              | Default value     |

| --------------------- | ---------------------------------------- | ----------------- |

| `unit-args` / `PHP_UNIT_ARGS` | Additional PHPUnit [options](https://docs.phpunit.de/en/11.0/textui.html#command-line-options) | _none_ |

| `unit-disabled` / `PHP_UNIT_DISABLED` | Set to `true` to disable PHPUnit test (if some `phpunit.xml` or `phpunit.xml.dist` file unintentionally triggers the build) | _none_ (auto based on presence of `phpunit.xml` or `phpunit.xml.dist` file) |

| `unit-disabled` / `PHP_UNIT_DISABLED` | Set to `true` to disable PHPUnit test | _none_ (auto based on presence of `phpunit.xml` or `phpunit.xml.dist` file) |

:warning: in order to be able to compute [code coverage](https://docs.phpunit.de/en/11.0/code-coverage.html),

your project shall have a (dev) dependency to [`php-code-coverage`](https://github.com/sebastianbergmann/php-code-coverage).