Don't run the "trusted" checks if we're in a PR (#85)

* Don't run the "trusted" checks if we're in a PR

* Apply suggestions from code review

* Update ci.yml

* Update ci.yml

.github/workflows/ci.yml

@@ -1,6 +1,7 @@
 name: CI
 
 on:
+  merge_group:
   pull_request:
   push:
     branches: [main]
@@ -95,16 +96,20 @@ jobs:
             runner: "ubuntu-22.04"
     steps:
       - uses: actions/checkout@v4
+        if: github.event_name == 'merge_group'
       - name: Install Nix on ${{ matrix.systems.nix-system }} system
+        if: github.event_name == 'merge_group'
         uses: DeterminateSystems/nix-installer-action@main
         with:
           flakehub: true
           extra-conf: |
             narinfo-cache-negative-ttl = 0
       - name: Cache the store
+        if: github.event_name == 'merge_group'
         uses: ./
         with:
           _internal-strict-mode: true
       - name: Check the cache for liveness
+        if: github.event_name == 'merge_group'
         run: |
           .github/workflows/cache-test.sh