More than 500 chars in attempted Matodon post

[sentry-io]

Perhaps some kind of difference in what we consider characters vs what Mastodon does?

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Sentry Issue: BIGCASES2-2M

MastodonAPIError: ('Mastodon API returned error', 422, 'Unprocessable Entity', 'Validation failed: Text character limit of 500 exceeded')
(6 additional frame(s) were not displayed)
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  File "bc/subscription/tasks.py", line 379, in make_post_for_webhook_event
    api_post_id = api.add_status(message, image, files)
  File "bc/channel/utils/connectors/masto.py", line 107, in add_status
    api_response = self.api.status_post(message, media_ids=media_ids)