ci/eval: test aliases

Aliases do not add new packages, so basic evaluation with nix-env should
be enough and fairly quick.

.github/workflows/eval.yml

@@ -91,6 +91,25 @@ jobs:
           name: paths
           path: result/*
 
+  eval-aliases:
+    name: Eval nixpkgs with aliases enabled
+    runs-on: ubuntu-latest
+    needs: attrs
+    steps:
+      - name: Check out the PR at the test merge commit
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          ref: ${{ needs.attrs.outputs.mergedSha }}
+          path: nixpkgs
+
+      - name: Install Nix
+        uses: cachix/install-nix-action@08dcb3a5e62fa31e2da3d490afc4176ef55ecd72 # v30
+
+      - name: Query nixpkgs with aliases enabled to check for basic syntax errors
+        id: systems
+        run: |
+          time nix-env -I ./nixpkgs -f ./nixpkgs -qa '*' --meta --option restrict-eval true --option allow-import-from-derivation false >/dev/null
+
   outpaths:
     name: Outpaths
     runs-on: ubuntu-latest