Twenty Twenty-Five: The Written by pattern on single posts has too low color contrast in some variations

Morning style variation, with section style 5 applied to the main group. The "written by" text is not readable.

Fixes #62982

### Testing instructions:

1. Activate Twenty Twenty-Five.
2. Edit the single posts template.
3. Select the main group block, or, the first group block that is inside the main.
4. Open the Styles tab in the block settings.
5. Apply Styles 1 to 5, one by one, and observe the color of the text
6. "Written by author in categories" that is below the featured image.

Test Report

Description

This report validates whether the indicated patch works as expected.

Patch tested: ​https://github.com/WordPress/wordpress-develop/pull/8347

Environment

• WordPress: 7.0-alpha-61215-src
• PHP: 8.2.29
• Server: nginx/1.29.3
• Database: mysqli (Server: 8.4.7 / Client: mysqlnd 8.2.29)
• Browser: Chrome 142.0.0.0
• OS: macOS
• Theme: Twenty Twenty-Five 1.3
• MU Plugins: None activated
• Plugins:
  • Test Reports 1.2.1

Actual Results

This issue has been solved with this patch

Screenshots

Before	After

Test Report

Description

Patch tested: ​https://github.com/WordPress/wordpress-develop/pull/8347.diff

• WordPress: 6.9-beta3-61129-src
• PHP: 8.4.12
• Server: nginx/1.29.1
• Database: mysqli (Server: 9.4.0 / Client: mysqlnd 8.4.12)
• Browser: Chrome 142.0.0.0
• OS: macOS
• Theme: Twenty Twenty-Five 1.3
• MU Plugins: None activated
• Plugins:
  • Test Reports 1.2.0

Actual Results

1. ✅ Issue resolved with patch.

Screenshots

Before Apply Patch	After Apply Patch ✅

I'm switching to enhancement because ​PR 103 purposely used a lighter color for the post meta text row. The text is also smaller and inherits the Light 300 weight, so the Default gray is not easy for me to read (even though the contrast ratio is AA-compliant at 5.57:1).

Accent 4 can be a problem if the chosen section style variation (e.g., Style 1, Style 2) is significantly different than the site's style variation (e.g., Evening, Dusk). The contrast is not a problem when the section styles are not used, and even the Style 2 and Style 3 options can have enough contrast in Midnight.

My testing process below confirmed that updating the template should not affect existing sites, leaving the original design for them.

1. Create a new site with WordPress 6.9, which already has Twenty Twenty-Five activated.
2. Go to the Editor and select the Single Posts template.
3. Find the Group block for the main post content. (I clicked on the "Written by" text, and then selected the second Group block in the breadcrumbs "Template > Group > Group > Row > Paragraph".)
4. View the block's Styles tab in the sidebar, and select Style 4 (or Style 5).
5. Save.
6. Create a theme update.
   • Apply the patch to another site, ideally a local installation.
   • Change the theme version number in readme.txt and style.css.
   • Compress the theme to a zip package. (I saved the package as twentytwentyfive.1.4.1.zip.)
7. Go back to the new site.
8. Go to Appearance > Themes, and click Add Theme.
9. Click Upload Theme, select the theme zip package, and click Install Now.
10. Click the "Replace installed with uploaded" button.
11. Go to the Editor and select the Single Posts template again, and check whether the Row block still has Accent 4 as the text color.

@sabernhardt I think I'll disagree with you on switching this to an enhancement, for two reasons:

1) It is a clear accessibility violation, and we have generally considered those to be bugs, regardless of prior intent and
2) The person who authored and merged that PR is the same person who opened this ticket, considering it to be a bug.

Thanks for confirming the impact on existing sites, as that's something that feels uncertain to me with patterns, sometimes...

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