Ak/clean up hub_validation print output. Deprecate file_modification_check argument "warn"

[annakrystalli]

This PR cleans up a few rough edges from the previous two PRs

• Changed file name header colour in hub_validations object print() method from br_cyan to magenta to make more visible on lighter backgrounds.
• Soft deprecated file_modification_check argument "warn" option and replaced it with "failure" in validate_pr() function. Also I updated the output documentation so reflect the new error/check_failure class.

[github-actions]

🚀 Deployed on https://66daee9a2b43eb11d308460f--hubvalidations-pr-previews.netlify.app

[zkamvar]

This looks good to me.

My only comment is to remove the coloring from the heading class since the surrounding dashes and underline distinguish it from the other content.

[annakrystalli]

Thanks for the review @zkamvar ! I tried it with the colour removed but I feel it still adds some useful contrast so I've left it for now.

[zkamvar]

I tried it with the colour removed but I feel it still adds some useful contrast so I've left it for now.

It's minor, but it will be a good idea to revisit this decision because it may be an accessibility issue in the future.