Use variables instead of secrets

Secrets are not available to forks. Using variables allows PRs CI runs to obtain the token as well.

Co-authored-by: per1234 <[email protected]>

Author: cmaglie

Diff for: .github/workflows/test-go-task.yml

@@ -197,7 +197,7 @@ jobs:
       - name: Send unit tests coverage to Codecov
         uses: codecov/codecov-action@v3
         with:
-          token: ${{ secrets.CODECOV_TOKEN }}
+          token: ${{ vars.CODECOV_TOKEN }}
           files: ./coverage.txt
           flags: unit
           fail_ci_if_error: ${{ github.repository == 'arduino/arduino-cli' }}