The Pull Request resource doesn't include the `comments` field, while
the Issue resource does. And since we're looping through all issues
anyway, we can freely check if the issue is a PR and has comments and in
this case only fetch comments for it.

That means if you have 1000 PRs but only 200 with comments, you will do
200 API requests instead of 1000. :notbad:
Signed-off-by: Rémy Coutable <remy@rymai.me>