The Scrum Guide states that the Scrum Master is "responsible for promoting and supporting Scrum as defined in the Scrum Guide" and that the Scrum Master has "accountability over the Scrum process". Since transparency is a key pillar of Scrum, I would interpret all of this to mean that the Scrum Master is accountable for the transparency of the artifacts. However, the Scrum Master likely won't do all of the work to make the artifacts transparent.
Ideally, transparency should "fall out" of the team's way of working and the tools that the team chooses to use to support their way of working. But that's not entirely possible all the time. I would suspect that the Scrum Master chooses to treat instances where the team needs to do additional work for the sake of transparency as an impediment to be resolved. This may mean that the Scrum Master becomes responsible for particular pieces of work, but it could also be delegated to others.
If the Scrum Master is responsible for work, I would be cautious of the Scrum Master becoming a secretary for the team. That is, the Scrum Master should not exist to update status boards or issue trackers or generate metrics or write reports. The Scrum Master should be focused on facilitating, teaching, and coaching. Anything else should be a stop-gap until better solutions can be put into place that don't put added responsibilities onto the role of the Scrum Master.
So, in short: Definitely accountable, but may be responsible for some elements of transparency.