[Identity] Add --no-prompt flag to AzureDeveloperCliCredential to prevent hanging with AZD_DEBUG

[Copilot]

When the AZD_DEBUG environment variable is set, the azd auth token subprocess hangs indefinitely waiting for user input:

$ AZD_DEBUG=1 azd auth token --output json --scope https://search.azure.com/.default
? Debugger Ready? (pid: 259503) (Y/n)

This causes AzureDeveloperCliCredential.get_token() to timeout when debugging is enabled.

This PR adds the --no-prompt flag to the azd auth token command to prevent interactive prompts and ensure the credential works reliably regardless of debug settings.

Changes:

• Added --no-prompt to the azd command construction in get_token()
• Updated test assertions to verify the flag is included in generated commands

Example command before:

azd auth token -o json --scope https://management.azure.com/.default

Example command after:

azd auth token -o json --no-prompt --scope https://management.azure.com/.default

All existing tests pass and the change is backward compatible.

Fixes #2910.

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