Include axe checks in `ee/spec/features/boards/new_issue_spec.rb`

What does this MR do and why?

As a part of moving towards adding accessibility checks for the product , adding accessibility checks for ee/spec/features/boards/new_issue_spec.rb. Closes Include axe checks in `ee/spec/features/boards/... (#433229)

Added the scope to boards-list data selector since the other error was adding a page level heading which is not required as per the designs of boards and maybe require more design discussions

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

No UI changes , just the color of list count changed to $gray-600 from gl-text-secondary for screen readability.

How to set up and validate locally

Run the test locally , it should pass

bin/rspec ee/spec/features/boards/new_issue_spec.rb

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Fixes Include axe checks in `ee/spec/features/boards/... (#433229)