fix(VDataTable): fix default table header color

[afzalsayed96]

Description

#9766 introduced a bug causing all headers of data-table to be of primary text color instead of only active or hovered ones.

See: https://vuetifyjs.com/en/components/data-tables#usage

Motivation and Context

IMO only active or hovered headers should be of primary text color as it used to be before v2.2

How Has This Been Tested?

visually

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)
• Improvement/refactoring (non-breaking change that doesn't add any features but makes things better)

Checklist:

• The PR title is no longer than 64 characters.
• The PR is submitted to the correct branch (master for bug fixes and documentation updates, dev for new features and breaking changes).
• My code follows the code style of this project.
• I've added relevant changes to the documentation (applies to new features and breaking changes in core library)
• I've added new examples to the kitchen (applies to new features and breaking changes in core library)

[MajesticPotatoe]

great catch! 👍
Thank you for your contribution and interest in improving Vuetify! Make sure to join us in the Discord community.

[afzalsayed96]

Thanks. Great work by Vuetify team!