9ac55a8cf6 introduced support for
batch updates to stories. However, that commit didn't skip label
removals, as we already do in non-batch story payloads. This led
to an exception for batch story update payloads where labels were
removed but none were added.
As the user can select multiple stories and edit multiple
properties at the same time, this can generate requests
without a "primary_id" containing multiple actions, while
each action contains multiple changes.
Fixes: #18022
The fixture "story_update_add_github_pull_request" is changed here as it
doesn't make sense to link a story to a PR without having "pull_request_ids"
changed. The previous example is likely a mistake which occurs when you try
to add a PR that has already been added to a story. This commit also allows
comments under the PR that link it to a story to be sent to the stream.
Fixes: #18022
Apparently, Clubhouse has two different payloads for story label
changes, one where the label name lives inside the "references"
object, and the other where it lives inside the "actions" object.
Their webhook API is still in beta, so this could just be a bug.
Anyhow, we should support both.