CI: also try to build frontend

Author: Twey

.github/workflows/main.yml

@@ -12,7 +12,7 @@ env:
   RUSTFLAGS: -D warnings
 
 jobs:
-  backend:
+  test:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
@@ -52,6 +52,12 @@ jobs:
       - name: 'Verify that code-generated files are unchanged'
         run: git diff --exit-code
 
+      - name: Build frontend
+      - run: |
+          cd frontend
+          pnpm install
+          pnpm build
+
   lint-cargo-fmt:
     runs-on: ubuntu-latest
     steps: