Fix unit test for reserved prefixed

Summary:
Github CI action failed: https://github.com/facebook/capi-param-builder/actions/runs/21370508022/job/61516057214

With investigation, seems 2001:db8::/32 prefix is reserved for IPv6 documentation prefix within [RFC3849](https://datatracker.ietf.org/doc/html/rfc3849). It should treat as a non-public IP.

However, this is a PHP bug. Th bug got fixed finally [patch](https://bugs.php.net/bug.php?id=61700#:~:text=History&text=The%20FILTER_FLAG_NO_RES_RANGE%20flag%20only%20works,nothing%20is%20done%20with%20it?&text=Hellon%20The%20problem%20is%20still,Thanks.). It got refactorred and released in 8.4.3([here](php/php-src#16944)). For pre-8.4.3 may carry over this bug.

For our use case, we want to valid and test a real public IP. Change the test case to a general public ipv6 ip.

Differential Revision: D91510128

fbshipit-source-id: a3f9d9f890ebb914ce374ad9ca875ad2bb49eb84

Author: hongj-src

php/capi-param-builder/tests/GetClientIpTest.php

@@ -116,8 +116,8 @@ public function testGetClientIpIPv6PublicPrioritization()
         $this->assertEquals(self::IPV6_PUBLIC . '.' . $this->appendix_no_change, $result);
 
         // IPv6 public from cookie should beat IPv6 public from request (cookie priority)
-        // Since request has a public IP, use APPENDIX_MODIFIED_NEW
-        $anotherIPv6Public = '2001:db8::1';
+        // Cloudflare DNS as public IP, use APPENDIX_MODIFIED_NEW
+        $anotherIPv6Public = '2606:4700:4700::1111';
         $result = $this->invokePrivateStaticMethod(
             'getClientIp',
             [FBI_NAME => self::IPV6_PUBLIC],