Switch from using Bors to merge queue in CI

.github/workflows/rust.yml

@@ -1,11 +1,8 @@
 name: Rust
 
 on:
-  push:
-    branches-ignore:
-      - trying.tmp
-      - staging.tmp
   pull_request:
+  merge_group:
 
 jobs:
   miri:
@@ -79,14 +76,12 @@ jobs:
           channel: stable
 
   # These jobs doesn't actually test anything, but they're only used to tell
-  # bors the build completed, as there is no practical way to detect when a
-  # workflow is successful listening to webhooks only.
+  # the merge queue the build completed.
   #
   # ALL THE PREVIOUS JOBS NEED TO BE ADDED TO THE `needs` SECTION OF THIS JOB!
 
   end-success:
-    name: bors build finished
-    if: github.event.pusher.name == 'bors' && success()
+    name: build finished
     runs-on: ubuntu-latest
     needs: [miri, rustfmt_clippy, test]
 
@@ -95,8 +90,8 @@ jobs:
         run: exit 0
 
   end-failure:
-    name: bors build finished
-    if: github.event.pusher.name == 'bors' && (failure() || cancelled())
+    name: build finished
+    if: failure() || cancelled()
     runs-on: ubuntu-latest
     needs: [miri, rustfmt_clippy, test]