added codcov token; impossible to one-shot it with CI :/

.github/workflows/build_env_run_tests.yml

@@ -16,16 +16,14 @@ jobs:
         uses: actions/setup-python@v4
         with:
           python-version: 3.11
-      - name: Set up environment
+      - name: Set up environment, run tests.
         run: |
           python -m venv env
           source env/bin/activate
           python -m pip install -e .
-      - name: Pytest with coverage report
-        run: |
           python -m pytest -n auto --cov=nanogpt --cov-report=xml
       - name: Upload test coverage report to codecov
-        uses: codecov/codecov-action@v3
+        uses: codecov/codecov-action@v4
         with:
           token: ${{ secrets.CODECOV_TOKEN }}
           file: ./coverage.xml