mscbot may not start FCP when using `@mscbot reviewed`

One can use `@mscbot reviewed` to automatically check the box for themselves in an ongoing FCP status comment. The bot will also unconditionally ignore all comments and comment edits from itself.

When designing the `reviewed` command, it was incorrectly assumed that updating the status comment would then have the knock-on effect of starting FCP if enough ticks had happened. Instead, the edit is ignored as it comes from the bot.

A fix would simply involve manually calling `_process_status_comment_update_with_body` below https://github.com/matrix-org/mscbot-python/blob/fd6027708fd6ce08767556689470a6759c8af4ef/command_handler.py#L169-L172

Start in command_handler.py around lines 169–172 and trace the reviewed command's handling of the ongoing FCP status comment. Ensure the bot's status-comment update is processed so that FCP starts when enough ticks have occurred, then verify the behavior with the project's relevant tests.

Written by the indexing model from the issue text.