x/build/cmd/gerritbot: inline comments not synchronized to GitHub

[tklauser]

What did you do?

1. Opened tklauser: add my own main.go scratch#35 which got imported into Gerrit as https://go-review.googlesource.com/c/scratch/+/230213
2. Replied with an inline code comment on the CL in Gerrit: https://go-review.googlesource.com/c/scratch/+/230213/1/tklauser/main.go#6

What did you expect to see?

Inline code comment synchronized to the GitHub PR by GerritBot.

What did you see instead?

GerritBot posted a comment to the PR, but the comment content was not added: golang/scratch#35 (comment)

Also, "global" reply comments on the CL get posted properly to the GitHub PR, see the "Testing with a CL comment" message https://go-review.googlesource.com/c/scratch/+/230213/2#message-7705eb20fe25b49c54c2c928532651e83a4e118f which got posted as golang/scratch#35 (comment)