UHF-X: Finetune black-60 to be AAA accessible against white

[Arkkimaagi]

UHF-X

• The current HDS Black-60 color of #666666 is not AAA accessible

See the timestamp of this page:

What was done

• I had a meeting with HDS and Hki Brand people and we agreed that this color change is reasonable and approved.

(Yes, the change is quite subtle)

How to install

• Make sure your instance is up and running on latest dev branch.
  • git pull origin dev
  • make fresh
• Update the HDBT theme
  • composer require drupal/hdbt:dev-UHF-X_finetune_grey60
• Run make drush-cr

How to test

• Check that the color used is now #595959 instead of #666666
• Check that code follows our standards

Designers review

• This PR does not need designers review
• This PR has been visually reviewed by a designer (Name of the designer)

[github-actions]

⚠️ Visual regression found! Please check if this change is wanted or accidental. You can check the output here: https://city-of-helsinki.github.io/drupal-hdbt/pull/924/html_report/

[teroelonen]

This works well 🦖