chore: add Codecov token to CI workflow for coverage uploads

Author: adrida

.github/workflows/ci.yml

@@ -28,4 +28,6 @@ jobs:
       run: |
         pytest tests/ --cov=tarmac --cov-report=xml
     - name: Upload coverage to Codecov
-      uses: codecov/codecov-action@v3 
+      uses: codecov/codecov-action@v3
+      with:
+        token: ${{ secrets.CODECOV_TOKEN }}