Specify CodeCov upload token

v4 of the CodeCov GitHub action no longer supports tokenless uploading.

Author: wimpyprogrammer

.github/workflows/continuous-integration.yml

@@ -47,4 +47,6 @@ jobs:
       - name: Upload test coverage report to Codecov
         uses: codecov/codecov-action@v4.1.0
         with:
-          fail_ci_if_error: false
+          fail_ci_if_error: true
+        env:
+          CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}