feat: quarantine upstream update candidates

.github/workflows/nightly-ci.yml

@@ -0,0 +1,32 @@
+name: Nightly Candidate
+
+on:
+  pull_request:
+    branches: [main]
+
+permissions:
+  contents: read
+
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+      - name: Detect nightly pin changes
+        id: nightly
+        env:
+          BASE_SHA: ${{ github.event.pull_request.base.sha }}
+          HEAD_SHA: ${{ github.event.pull_request.head.sha }}
+        run: |
+          if git diff --quiet "$BASE_SHA" "$HEAD_SHA" -- nightly.nix; then
+            echo "changed=false" >>"$GITHUB_OUTPUT"
+          else
+            echo "changed=true" >>"$GITHUB_OUTPUT"
+          fi
+      - if: steps.nightly.outputs.changed == 'true'
+        uses: DeterminateSystems/nix-installer-action@v13
+      - name: Build nightly compatibility suite
+        if: steps.nightly.outputs.changed == 'true'
+        run: nix build .#legacyPackages.x86_64-linux.nightlyChecks.all --accept-flake-config