test: run tests directly after build to see if they pass

.github/workflows/rust.yml

@@ -16,6 +16,10 @@ jobs:
     - uses: actions/checkout@v4
     - name: Build
       run: cargo build --verbose
+    - name: Run tests
+      env:
+        OPENAI_API_KEY: ${{ secrets.OPENAI_API_KEY }}
+      run: cargo test --verbose
 
   tests:
     runs-on: ubuntu-latest