[Identity] Add --no-prompt flag to AzureDeveloperCliCredential to prevent hanging with AZD_DEBUG (Azure#2914)

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

```shell
$ 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 Azure#2910.

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Co-authored-by: copilot-swe-agent[bot] <[email protected]>
Co-authored-by: heaths <[email protected]>

Author: Copilot

sdk/identity/azure_identity/src/azure_developer_cli_credential.rs

@@ -118,7 +118,7 @@ impl TokenCredential for AzureDeveloperCliCredential {
                 "at least one scope required",
             ));
         }
-        let mut command = OsString::from("azd auth token -o json");
+        let mut command = OsString::from("azd auth token -o json --no-prompt");
         for scope in scopes {
             validate_scope(scope)?;
             command.push(" --scope ");
@@ -170,12 +170,15 @@ mod tests {
                     if cfg!(target_os = "windows") {
                         assert_eq!(program.to_string_lossy(), "cmd");
                         assert_eq!(args[0], "/C");
-                        assert!(args[1]
-                            .starts_with(&format!("cd {system_root} && azd auth token -o json")));
+                        assert!(args[1].starts_with(&format!(
+                            "cd {system_root} && azd auth token -o json --no-prompt"
+                        )));
                     } else {
                         assert_eq!(program, "/bin/sh");
                         assert_eq!(args[0], "-c");
-                        assert!(args[1].starts_with("cd /bin && azd auth token -o json"));
+                        assert!(
+                            args[1].starts_with("cd /bin && azd auth token -o json --no-prompt")
+                        );
                     }
                     for scope in LIVE_TEST_SCOPES {
                         assert!(args[1].contains(&format!(" --scope {scope}")));