Prepare repo for enabling merge queue

.github/workflows/book.yml

@@ -3,6 +3,7 @@
 name: Build Book
 on:
   workflow_dispatch:
+  merge_group:
   pull_request:
     branches: [ main ]
   push:

.github/workflows/kani.yml

@@ -2,6 +2,7 @@ name: Kani
 
 on:
   workflow_dispatch:
+  merge_group:
   pull_request:
     branches: [ main ]
   push:

.github/workflows/pr_approval.yml

@@ -1,12 +1,14 @@
+# This workflow checks that the PR has been approved by 2+  members of the committee listed in `pull_requests.toml`.
+# Run this pull request when a request review is submitted / dismissed.
+# Note that an approval can be dismissed, and this can affect the job status.
+# We currently trust that contributors won't make significant changes to their PRs after approval, so we accept
+# changes after approval.
 name: Check PR Approvals
-
-# For now, the workflow gets triggered only when a review is submitted
-# This technically means, a PR with zero approvals can be merged by the rules of this workflow alone
-# To protect against that scenario, we can turn on number of approvals required to 2 in the github settings
-# of the repository
 on:
+  merge_group:
+  pull_request:
   pull_request_review:
-    types: [submitted]
+    types: [submitted, dismissed]
 
 jobs:
   check-approvals:
@@ -20,6 +22,7 @@ jobs:
 
       - name: Check PR Relevance and Approvals
         uses: actions/github-script@v6
+        if: ${{ github.event_name != 'merge_group' }}
         with:
           script: |
             const fs = require('fs');

.github/workflows/rustc.yml

@@ -4,6 +4,7 @@
 name: Rust Tests
 on:
   workflow_dispatch:
+  merge_group:
   pull_request:
     branches: [ main ]
   push: