Credits Shortcode: Remove trailing double slash from profile URLs

[huzaifaalmesbah]

Summary

• The [wpcredits] shortcode was generating profile URLs with a double trailing slash (//), e.g. https://profiles.wordpress.org/username//
• The profiles URL template in wp-credits.php already includes a trailing slash (%s/), so the extra / appended in shortcode.php was redundant
• Removed the unnecessary / concatenation from the anchor href output

Test plan

• Use the shortcode [wpcredits 7.0 class="has-small-font-size" exclude="ideag"] on a page
• Verify that profile links now render as https://profiles.wordpress.org/{username}/ (single trailing slash)
• Verify links still work and redirect correctly to user profiles

[Copilot]

Pull request overview

This PR fixes malformed contributor profile links generated by the [wpcredits] shortcode by removing an extra trailing slash that resulted in // at the end of profile URLs.

Changes:

• Remove redundant '/’ concatenation when building contributor profile links so the existing %s/ URL template is used as-is.

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Props huzaifaalmesbah.

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