Update image chooser tests for Wagtail 7's default_alt_text response key

Wagtail 7.x adds a default_alt_text field to the image chooser chosen-step
response payload (sourced from the new Image.description model field).
The three TestImageChosenView assertions exhaustively compared the JSON
response, so they regressed once Wagtail started emitting the extra key.

Allow the new key with mock.ANY, matching the existing handling of the
preview value.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: nickmoreton

tests/test_image_chooser_views.py

@@ -51,6 +51,7 @@ def test_creates_image_if_asset_id_not_recognised(self):
                     "title": image.title,
                     "preview": mock.ANY,
                     "edit_url": reverse("wagtailimages:edit", args=[image.id]),
+                    "default_alt_text": mock.ANY,
                 },
             },
         )
@@ -78,6 +79,7 @@ def test_uses_existing_image_without_updating(self, update_object_mock):
                     "title": image.title,
                     "preview": mock.ANY,
                     "edit_url": reverse("wagtailimages:edit", args=[image.id]),
+                    "default_alt_text": mock.ANY,
                 },
             },
         )
@@ -105,6 +107,7 @@ def test_uses_existing_image_and_updates_it(self, update_object_mock):
                     "title": image.title,
                     "preview": mock.ANY,
                     "edit_url": reverse("wagtailimages:edit", args=[image.id]),
+                    "default_alt_text": mock.ANY,
                 },
             },
         )