[release/10.0] Backport Replace test certificate chain that uses RSA+SHA-1

[vcsjones]

Backport of #121450 to release/10.0

cc @bartonjs

Customer Impact

These are test only changes. These changes react to more environments in CI rejecting certificate chains that use an RSA+SHA-1 root certificate.

• Customer reported
• Found internally

Regression

• Yes
• No

Testing

Tests that were failing are now passing in CI.

Risk

None, test only changes.

[dotnet-policy-service]

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[vcsjones]

For what it’s worth this backported cleanly, but the backport command could not backport from a fork because my fork had some refs that were not available in the runtime repository. The patch applied just fine when both remotes were in the index.

[Copilot]

Pull Request Overview

This PR backports certificate test data updates from the main branch to release/10.0, replacing an RSA+SHA-1 certificate chain (Baltimore CyberTrust Root) with an RSA+SHA-256 certificate chain (DigiCert Global Root G2) to address CI test failures due to increasing SHA-1 rejection in test environments.

• Updates test certificate chain from Baltimore CyberTrust Root to DigiCert Global Root G2
• Adjusts test data including hostnames, verification times, and expected cryptographic values
• Removes platform-specific workarounds no longer needed with the new certificate

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
MatchesHostnameTests.cs	Updates test hostnames to match SANs in new certificate (e.g., www.microsoft.com.au, copilot.ai, yarp.dot.net)
AuthorityKeyIdentifierTests.cs	Updates expected authority key identifier hex values to match new certificate chain
CollectionTests.cs	Updates verification times from 2021-02-26 to 2025-12-25 to fall within new certificate validity period
ChainTests.cs	Updates verification times throughout tests, removes SHA-1 signature support checks, simplifies platform detection logic
TestData.cs	Replaces MicrosoftDotComSslCertBytes, MicrosoftDotComIssuerBytes, and MicrosoftDotComRootBytes with new certificate chain data

[bartonjs]

@artl93 Test-only change