You cannot use the config property in dbt_project.yml. You should use flags instead:

Use flag warn_error

To transform all warnings to errors:

flags:
  warn_error: true

Use flag warn_error_options

To transform some flags to errors:

flags:
  warn_error_options:
    error: # Previously called "include"
      - NoNodesForSelectionCriteria
      - NothingToDo
    warn: # Previously called "exclude"
    silence: # To silence or ignore warnings

Sources:

• The code above is adapted from the Warning documentation of dbt: https://docs.getdbt.com/reference/global-configs/warnings
• List of all flags: https://docs.getdbt.com/reference/global-configs/about-global-configs#available-flags
• Definition of flags in dbt: https://docs.getdbt.com/reference/global-configs/about-global-configs