Lock major change issue

Author: Urgau

src/handlers/major_change.rs

@@ -294,6 +294,10 @@ async fn handle(
             .post_comment(&ctx.github, &comment)
             .await
             .context("post major change comment")?;
+        issue
+            .lock(&ctx.github, None)
+            .await
+            .context("lock major change issue")?;
     }
 
     let zulip_req = zulip_req.send(&ctx.github.raw());