Permalink: Fix search pagination 404 error when using numbered pagination

[im3dabasia]

Trac ticket: https://core.trac.wordpress.org/ticket/63123

Fix pagination links for search results by preventing trailing slashes from being added to search query parameters. This change preserves the functionality from changeset [59966] while preventing 404 errors specifically on search result pages.

The issue occurred because trailing slashes were being added after search query parameters (e.g., ?s=post/), causing malformed URLs. This change ensures numbered pagination works correctly on search pages while maintaining trailing slash consistency elsewhere like the categories page.

Screencast

Before:

https://github.com/user-attachments/assets/57231c79-5456-4759-ad09-fde5b196fff2

After:

https://github.com/user-attachments/assets/37c2bada-86db-4204-bd6a-d535783c1ee0