Prepare CI for merge queue

.github/workflows/check-nix-format.yml

@@ -6,6 +6,7 @@ name: Check that Nix files are formatted
 on:
   pull_request:
     types: [opened, synchronize, reopened]
+  merge_group:
 permissions:
   contents: read
 

.github/workflows/pr.yml

@@ -1,6 +1,7 @@
 name: "Test"
 on:
   pull_request:
+  merge_group:
   # For bors
   push:
     branches: