Add @bors rollup=never to rustc-push PR body

Author: Kobzol

Diff for: josh-sync/src/sync.rs

@@ -180,7 +180,7 @@ impl GitSync {
         );
         println!(
             // Open PR with `subtree update` title to silence the `no-merges` triagebot check
-            "    https://github.com/{UPSTREAM_REPO}/compare/{github_user}:{branch}?quick_pull=1&title=Rustc+dev+guide+subtree+update&body=r?+@ghost"
+            "    https://github.com/{UPSTREAM_REPO}/compare/{github_user}:{branch}?quick_pull=1&title=Rustc+dev+guide+subtree+update&body=@bors+rollup=never%0Ar?+@ghost"
         );
 
         drop(josh);