topic: fix the `topic(...)` revset to not select commits without a topic The problem seems to be that the now removed __contains__ check would select any revision indicated by a non-string argument. This led to `topic(head())` returning a bunch of non-topic heads, though not as many as simply `head()`. I'm likely misunderstanding something, because there appears to be a similar __contains__ check for `branch()` in core. But maybe that's just harder to see the issue, because branch names doesn't disappear like topics.