Enable proper code coverage

[nodeg]

Description

Enable proper code coverage with simplecov and then fix the code coverage report in the CI tests:

==> Running upload-coverage
      ./codecov upload-coverage --git-service github --sha 1f1a2fd0f88ecc92811dd09e332073fcd55ad17f --branch nodeg:ci_add_ruby34_tests --dir ./coverage --gcov-executable gcov
info - 2025-02-26 14:20:12,795 -- ci service found: github-actions
warning - 2025-02-26 14:20:12,800 -- No config file could be found. Ignoring config.
warning - 2025-02-26 14:20:12,818 -- xcrun is not installed or can't be found.
warning - 2025-02-26 14:20:12,819 -- No gcov data found.
warning - 2025-02-26 14:20:12,819 -- coverage.py is not installed or can't be found.
info - 2025-02-26 14:20:12,832 -- Found 0 coverage files to report
Error: No coverage reports found. Please make sure you're generating reports successfully.
Sentry is attempting to send 2 pending events
Waiting up to 2 seconds
Press Ctrl-C to quit
==> Failed to run upload-coverage