publish_toolstate.py: further fix the runtime errors
publish_toolstate.py: further fix the runtime errors

The regex was missing a `,`, causing `relevant_pr_match` to become None
and set the PR number to -1 and assigned the new issue to
`@<unknown user>`. This causes the 422 error when creating the issue due
to invalid assignee and unable to leave the tool-is-broken comment since
PR -1 does not exist.

The default user names are now also changed to @ghost to prevent the
422 error in case anything goes wrong again.

aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust