Update codecov action to v4, limit to latest version

Token is required for Codecov now

Only upload coverage report for latest version

(since the project should behave the same under every version)

.github/workflows/python-package.yml

@@ -56,4 +56,11 @@ jobs:
           pytest --cov=./ --cov-report=xml
 
       - name: Upload coverage to Codecov
-        uses: codecov/codecov-action@v3.1.1
+        if: matrix.python-version == '3.12'
+        uses: codecov/codecov-action@v4
+        with:
+          files: ./coverage.xml
+          fail_ci_if_error: true
+          verbose: true
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}