Fix Rich Media Previews for updated activities

The Rich Media Previews were not regenerated when a post was updated due to a cache invalidation issue. They are now cached by the activity id so they can be evicted with the other activity cache objects in the :scrubber_cache.

test/pleroma/web/rich_media/helpers_test.exs

@@ -83,6 +83,34 @@ defmodule Pleroma.Web.RichMedia.HelpersTest do
              Pleroma.Web.RichMedia.Helpers.fetch_data_for_activity(activity)
   end
 
+  test "recrawls URLs on updates" do
+    original_url = "https://google.com/"
+    updated_url = "https://yahoo.com/"
+
+    Pleroma.StaticStubbedConfigMock
+    |> stub(:get, fn
+      [:rich_media, :enabled] -> true
+      path -> Pleroma.Test.StaticConfig.get(path)
+    end)
+
+    user = insert(:user)
+    {:ok, activity} = CommonAPI.post(user, %{status: "I like this site #{original_url}"})
+
+    assert match?(
+             %{page_url: ^original_url, rich_media: _},
+             Pleroma.Web.RichMedia.Helpers.fetch_data_for_activity(activity)
+           )
+
+    {:ok, _} = CommonAPI.update(user, activity, %{status: "I like this site #{updated_url}"})
+
+    activity = Pleroma.Activity.get_by_id(activity.id)
+
+    assert match?(
+             %{page_url: ^updated_url, rich_media: _},
+             Pleroma.Web.RichMedia.Helpers.fetch_data_for_activity(activity)
+           )
+  end
+
   # This does not seem to work. The urls are being fetched.
   @tag skip: true
   test "refuses to crawl URLs of private network from posts" do