worker: hide previous comments when posting a new failure

Author: pietroalbini

src/bin/server/worker.rs

@@ -264,6 +264,7 @@ impl Worker {
         };
 
         let log_url = job.log_url().unwrap_or_else(|| "unknown".into());
+        self.github.hide_own_comments(repo, pr)?;
         self.github.post_comment(repo, pr, &format!(r#"
 {opening} failed! Check out the build log: [(web)]({html_url}) [(plain)]({log_url})