Update admin.sites._ViewType bound to allow StreamingHttpResponse (#2256)

* Update `admin.sites._ViewType` bound to allow `StreamingHttpResponse`

From the [Django documentation](https://docs.djangoproject.com/en/5.0/ref/request-response/#streaminghttpresponse-objects):
> The `StreamingHttpResponse` is not a subclass of `HttpResponse` ...

Because of this, creating an admin view that returned a
`StreamingHttpResponse` was causing the following Mypy error:

```
testing/admin.py:14: error: Value of type variable "_ViewType" of "admin_view" of "AdminSite" cannot be "Callable[[HttpRequest], StreamingHttpResponse]"  [type-var]
```

This updates the admin `_ViewType` type-var bound to allow a Callable
that can return a union of `HttpResponse | StreamingHttpResponse`.

After this update to the stubs file, the Mypy error is no longer
reproducible.

* Use `HttpResponseBase` common parent instead

Author: savanto

django-stubs/contrib/admin/sites.pyi

@@ -10,7 +10,7 @@ from django.core.checks import CheckMessage
 from django.db.models.base import Model
 from django.db.models.query import QuerySet
 from django.http.request import HttpRequest
-from django.http.response import HttpResponse
+from django.http.response import HttpResponse, HttpResponseBase
 from django.template.response import TemplateResponse
 from django.urls import URLPattern, URLResolver
 from django.utils.functional import LazyObject, _StrOrPromise
@@ -25,7 +25,7 @@ else:
 
     all_sites: MutableSet[AdminSite]
 
-_ViewType = TypeVar("_ViewType", bound=Callable[..., HttpResponse])
+_ViewType = TypeVar("_ViewType", bound=Callable[..., HttpResponseBase])
 _ModelT = TypeVar("_ModelT", bound=Model)
 _ActionCallback: TypeAlias = Callable[[ModelAdmin, HttpRequest, QuerySet], TemplateResponse | None]