Fix simulator test: resolve nixpkgs from npins for xcodegen

The iOS CI job doesn't set NIX_PATH, so `nix-shell -p xcodegen`
failed with "file 'nixpkgs' was not found in the Nix search path".
Resolve nixpkgs from npins inline, consistent with how the project
already handles nix dependencies.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jappeace-sloth

.github/workflows/ci.yaml

@@ -92,7 +92,9 @@ jobs:
     - name: Build simulator test
       run: nix-build nix/simulator.nix -o result-simulator
     - name: Run simulator lifecycle test
-      run: nix-shell -p xcodegen --run "./result-simulator/bin/test-lifecycle-ios"
+      run: |
+        NIXPKGS=$(nix-instantiate --eval -E 'builtins.toString (import ./npins).nixpkgs' | tr -d '"')
+        nix-shell -I "nixpkgs=$NIXPKGS" -p xcodegen --run "./result-simulator/bin/test-lifecycle-ios"
     - name: Upload iOS library
       if: github.ref == 'refs/heads/master'
       uses: actions/upload-artifact@v4

makefile

@@ -12,7 +12,7 @@ test-emulator:
 
 test-simulator:
 	nix-build nix/simulator.nix -o result-simulator
-	nix-shell -p xcodegen --run "./result-simulator/bin/test-lifecycle-ios"
+	nix-shell -I nixpkgs=$$(nix-instantiate --eval -E 'builtins.toString (import ./npins).nixpkgs' | tr -d '"') -p xcodegen --run "./result-simulator/bin/test-lifecycle-ios"
 
 haddock:
 	cabal haddock all