Fix condition for disabling colors in CLI output

Motivation and Context

Color disabling doesn't work on Gitlab pipeline. On the pipeline, TERM env var is unset (== ""), and in this case, the --no-color CLI flag was incorrectly ignored.

Description

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Performance improvement (non-breaking change that improves performance)
• None (change with no changelog)

Changelog

Using flag --no-color in CI can be ignored if variable TERM is not set. Here a fix to make --no-color flag valid even if TERM is not defined.

Checklist:

• Changes follow the existing coding style (use dune @fmt to check).
• Tests for the changes have been added (for bug fixes / feature).
• Documentation has been updated.
• Changelog description has been added (if appropriate).
• Start titles under ## Changelog section with #### (if appropriate).
• There is no image or uploaded file in changelog
• Examples in changed behaviour have been added to the changelog (for breaking change / feature).