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:
@@ -78,28 +75,16 @@ jobs:
           target: x86_64-unknown-linux-gnu
           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.
-  #
-  # 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()
-    runs-on: ubuntu-latest
-    needs: [miri, rustfmt_clippy, test]
-
-    steps:
-      - name: Mark the job as successful
-        run: exit 0
-
-  end-failure:
-    name: bors build finished
-    if: github.event.pusher.name == 'bors' && (failure() || cancelled())
+  conclusion:
+    # https://github.com/rust-lang/rustup/blob/a9c4362a1b256ce56ef6a567b0ce46a474b8cd28/.github/workflows/ci.yaml
+    if: always()
+    needs: [test]
     runs-on: ubuntu-latest
-    needs: [miri, rustfmt_clippy, test]
-
     steps:
-      - name: Mark the job as a failure
-        run: exit 1
+      - name: Conclusion
+        run: |
+          jq -C <<< "${needs}"
+          # Check if all needs were successful or skipped.
+          "$(jq -r 'all(.result as $result | (["success", "skipped"] | contains([$result])))' <<< "${needs}")"
+        env:
+          needs: ${{ toJson(needs) }}