Replace mock Game Center Certificate with updated Digicert certificate URL

New Issue Checklist

• I am not disclosing a vulnerability.
• I am not just asking a question.
• I have searched through existing issues.
• I can reproduce the issue with the latest version of Parse Server.

Issue Description

Game Center Certificates =< 4 (e.g https://static.gc.apple.com/public-key/gc-prod-4.cer) were signed by Symantec. Apple have been phasing out their support for Symantec issued certs, and they are now completely untrusted. This explains why they are no longer serving https://static.gc.apple.com/public-key/gc-prod-4.cer. Previously, we resolved this issue by mocking the response from the apple server.

The problem here though is that all the existing Game Center test cases use a Symantec issued certificate. Test cases seem to be generated thanks to cloud.xtralife.gamecenterauth, however they haven't updated their code to use a valid Digicert certificate.

Steps to reproduce

Update test cases to use updated Game Center certificate (https://developer.apple.com/forums/thread/686122)

Actual Outcome

Signing failed

Expected Outcome

Tests should be updated with Digicert signed certificate. Test signature, salt and bundle ID will need to be valid in order for the signing to work (hence why we are using cloud.xtralife.gamecenterauth)

Environment

Server

• Parse Server version: alpha
• Operating system: macos
• Local or remote host (AWS, Azure, Google Cloud, Heroku, Digital Ocean, etc): remote

Logs

Locate the existing Game Center test cases and review the referenced cloud.xtralife.gamecenterauth test_gamecenter.js data, then compare the certificate URL with Apple's developer guidance. Update the tests to use a valid Digicert certificate and matching signature inputs, and run the Game Center tests to confirm signing succeeds.