Fix audience URLs for AzureGovernment and AzureChina to align with Azure CLI

[AzureMarker]

• The purpose of this PR is explained in this or a referenced issue.
• The PR does not update generated files.
  • These files are managed by the codegen framework at Azure/autorest.go.
• Tests are included and/or updated for code changes.
• Updates to module CHANGELOG.md are included.
• MIT license headers are included in each file.

This PR fixes #25700

[Copilot]

Pull request overview

This PR fixes audience URL inconsistencies for AzureGovernment and AzureChina cloud configurations by adding trailing slashes to align with Azure CLI, other SDKs, and the existing AzurePublic configuration.

Key Changes:

• Added trailing slashes to cloud.AzureChina and cloud.AzureGovernment audience URLs
• Updated CHANGELOG.md to document the bug fix

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
sdk/azcore/arm/runtime/runtime.go	Added trailing slashes to audience URLs for AzureChina and AzureGovernment to match AzurePublic and align with Azure CLI
sdk/azcore/CHANGELOG.md	Added entry documenting the bug fix for audience values in version 1.20.1

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Review Summary: No issues found. The changes correctly fix the audience URL inconsistency by adding trailing slashes to AzureChina and AzureGovernment configurations, making them consistent with the existing AzurePublic configuration. The existing test coverage in pipeline_test.go validates these audience URLs and will continue to work correctly with the trailing slashes, as the test constructs scopes by appending "/.default" to the audience URL.