Add a note on branches-ignore

Author: blaginin

.github/workflows/rust.yml

@@ -19,6 +19,9 @@ name: Rust
 
 on:
   push:
+    # When PR is in the Merge Queue, GitHub will create a temporary branch - but we already have a
+    # CI running because of `merge_group`
+    # https://github.com/orgs/community/discussions/15254
     branches-ignore:
       - 'gh-readonly-queue/**'
   pull_request: