docs: arbitrary_types_allowed needed in Pydantic example

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### Describe the bug

In https://yarl.aio-libs.org/en/latest/#why-isn-t-boolean-supported-by-the-url-query-api it is stated that:

> The [URL](https://yarl.aio-libs.org/en/latest/api/#yarl.URL) could be used as a field type in [pydantic](https://docs.pydantic.dev/latest/) models seamlessly:
>
> ```py
> from pydantic import BaseModel
> from yarl import URL
>
> class Model(BaseModel):
> url: URL
> ```

However, the example does not work out of the box:

```
PydanticSchemaGenerationError: Unable to generate pydantic-core schema for . Set `arbitrary_types_allowed=True` in the model_config to ignore this error or implement `__get_pydantic_core_schema__` on your type to fully support it.

If you got this error by calling handler() within `__get_pydantic_core_schema__` then you likely need to call `handler.generate_schema()` since we do not call `__get_pydantic_core_schema__` on `` otherwise to avoid infinite recursion.

For further information visit https://errors.pydantic.dev/2.12/u/schema-for-unknown-type
```

The working example would be:

```py
In [20]: class C(pydantic.BaseModel):
...: model_config = pydantic.ConfigDict(arbitrary_types_allowed=True)
...: endpoint: yarl.URL
```

Versions tested:
```
In [23]: pydantic.__version__
Out[23]: '2.12.5'

In [24]: yarl.__version__
Out[24]: '1.22.0'

In [26]: sys.version
Out[26]: '3.10.11 (v3.10.11:7d4cc5aa85, Apr 4 2023, 19:05:19) [Clang 13.0.0 (clang-1300.0.29.30)]'
```

### To Reproduce

...

### Expected behavior

...

### Logs/tracebacks

```python-traceback
...
```

### Python Version

```console
In [26]: sys.version
Out[26]: '3.10.11 (v3.10.11:7d4cc5aa85, Apr 4 2023, 19:05:19) [Clang 13.0.0 (clang-1300.0.29.30)]'
```

### multidict Version

```console
In [28]: multidict.__version__
Out[28]: '6.7.1'
```

### propcache Version

```console
In [31]: propcache.__version__
Out[31]: '0.4.1'
```

### yarl Version

```console
In [24]: yarl.__version__
Out[24]: '1.22.0'
```

### OS

macOS

### Additional context

Pls consider simplifying the bug report form 🙏🏻