Update text color in minimal error view to ensure better accessibility

[FoksVHox]

This pull request makes a minor visual improvement to the error page template. The color of the error code and message text has been updated for better readability and dark mode support.

• Updated text color classes in src/Illuminate/Foundation/Exceptions/views/minimal.blade.php to use text-gray-600 for light mode and dark:text-gray-300 for dark mode, improving accessibility and visual consistency across themes.
• Ensured contrast ratios meet WCAG AAA accessibility standards, making the error page more readable for all users, including those with visual impairments.

While developing my own application, and writing tests to ensure it would be accessible for all users, I found that the standard HTTP error pages were having issues with the contrast of the text color and background color.

Prior to these changes, when comparing the contrast ratios, it would be:

After these changes, when comparing the contrast ratios, it will be: