Fix coverage report (bayesian-optimization#552)

Author: till-m

.github/workflows/run_tests.yml

@@ -51,4 +51,6 @@ jobs:
       run: |
         poetry run pytest --cov-report xml --cov=bayes_opt/
     - name: Upload coverage to Codecov
-      uses: codecov/codecov-action@v3
+      uses: codecov/codecov-action@v4
+      with:
+          token: ${{ secrets.CODECOV_TOKEN }}