Fix alignment of plugin favorites username form

[deepakpra]

Trac ticket: https://core.trac.wordpress.org/ticket/65231

What?

Fixes the alignment of the username input and “Get Favorites” button on the Add Plugins > Favorites screen.

Why?

The plugin favorites form used plain paragraph markup, so the input and submit button were not vertically aligned.

How?

• Added the existing favorites-username class to the plugin favorites form row.
• Reused the existing flex alignment styles already used by the theme favorites form.

Testing

• Confirmed the input field and “Get Favorites” button align correctly on Plugins > Add New > Favorites.

Use of AI Tools

None

Screenshot

Before	After

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props deepakprajapati.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.

[deepakpra]

Closing this PR in favor of #11817 . I did not see the existing fix before opening this PR, and the issue is already addressed there.