[#17180] add missing link target

Author: xabbuh

security.rst

@@ -2714,3 +2714,4 @@ Authorization (Denying Access)
 .. _`SymfonyCastsVerifyEmailBundle`: https://github.com/symfonycasts/verify-email-bundle
 .. _`HTTP Basic authentication`: https://en.wikipedia.org/wiki/Basic_access_authentication
 .. _`Login CSRF attacks`: https://en.wikipedia.org/wiki/Cross-site_request_forgery#Forging_login_requests
+.. _`PHP date relative formats`: https://www.php.net/datetime.formats.relative