refactor: use poetry run in convert_test_files.sh test script

[omararvin]

This Make sure the following:

• The correct version of rmc (from the Poetry environment) is always executed
• The script works reliably in CI/CD pipelines
• The script works consistently across different developer machines

[Azeirah]

I think that in the end it would be best to convert the entire script to pytest, but this is a small win that can be merged immediately imo